in a Book
PRE-1992 VS. 1992-ON: Richard Mansell quotes from
a Jaguar publication describing the changes for the 1992
New cruise control:
The V12 models now feature the Hella speed control system
as fitted to the pre-92 MY 3.6 coupe in place of the AE
Econcruise system. This gives more logical layout, more
accurate control of speed, the addition of a cancel
As of now, this book only addresses the pre-1992 cruise
PRE-1992 CRUISE CONTROL: Thanks for the following
procedures for troubleshooting the Jaguar cruise control
system go mainly to Tom D. Graham.
CRUISE CONTROL DESCRIPTION: An electrical signal
from the drive train provides the signal about how fast the
car is going. On early XJ-S's there was a dedicated sending
unit near the input flange on the differential unit. Later
XJ-S's split a signal from the speedometer transducer on the
transmission. On still later models, reportedly the
transducer is built into the differential unit itself.
The signal is processed by the cruise control electronic
speed control unit. The speed control unit directs the
amount of vacuum in the bellows unit and the bellows unit
operates a cable to the gas pedal/throttle.
Within the bellows assembly are two solenoids, one which
normally (cruise control off) vents the bellows to
atmosphere and the other which normally seals off the vacuum
line from the intake manifold. The "vent solenoid" is
connected to the yellow/white and black wires, and the
"vacuum solenoid" is connected to the yellow/white and
yellow/black wires. When the control unit calls for speeding
the car up, 12V is applied to the yellow/white wire,
activating both solenoids. The vent is sealed and the vacuum
line is opened, and the resulting vacuum within the bellows
pulls the cable, applying throttle. The speed control unit
modulates the ground connection of the vacuum solenoid to
apply the proper vacuum to maintain a constant speed.
On the brake pedal housing is a switch that breaks the
yellow/white wire whenever the brakes are applied,
effectively shutting off the system and allowing the
throttle to return to idle. This is actually a back-up
feature; the power from the brake light switch is also sent
to the speed control unit, which is supposed to drop the
power to the yellow/white wire.
As the result of a recall, there is yet another back-up
device installed in the vacuum line to the bellows unit.
This device is designed to seal the vacuum line and vent the
bellows unit in addition to the solenoids.
CRUISE CONTROL ADJUSTMENT: If the cruise control
is adjusted correctly, when the set switch is pressed the
system will maintain the speed the car was doing at the
instant the button was pressed. If adjusted incorrectly, it
will maintain either a higher or lower speed. Hence, the
test procedure is drive the car on a straight and level road
and press the set switch, allow the speed to settle about
ten seconds, and press it again. If adjusted properly, it
can be set over and over and still maintain the same speed.
If incorrectly, the repeated sets will result in gradually
higher or lower speeds.
If adjusted incorrectly, adjust the speed control unit
until correct; it is a simple matter to have the speed
control unit hanging under the dash (it is located above the
passenger side footwell) and the necessary tools along for
the test drive, and possibly even an assistant driving.
Although the repair manual describes a method of adjusting
the cruise control, some of these units have no obvious
adjustments. If you pry the box open, however, there are two
adjustable pots on the circuit board. The one to adjust is
the one in the corner, farthest from where the wires enter
the box. NOTE: The adjuster is very sensitive; it is
difficult to move it a small enough increment.
CRUISE CONTROL TROUBLESHOOTING -- BELLOWS UNIT: If
you have an ohmmeter, check the resistance across the
bellows solenoids, yellow/white to black and yellow/white to
yellow/black. Each solenoid should register 25-30 ohms.
Unplug the connector to the bellows unit, and connect the
black wire from the unit to chassis ground and the
yellow/white wire to 12V using a jumper wire. You should
hear a click. Disconnect the black wire from ground and
connect the yellow/black wire to ground, and once again
connect the yellow/white wire to 12V. You should hear
another click. This verifies that both solenoids are
Connect both the black and yellow/black wires to ground
and the yellow/white to 12V to activate both solenoids, and
suck on a hose connected to the bellows unit. You should be
able to move the bellows. If you can't seem to suck
anything, the vacuum solenoid isn't opening (or the hose is
kinked or plugged). If you seem to suck air easily without
accomplishing anything, either the vent solenoid isn't
closing or the assembly is leaking.
The following comments apply to the older cruise control
actuators that had a bellows that looked like a bellows, and
a flat metal disk that the cable attached to. Newer cars use
a different actuator, and some even attach directly to the
bellcrank -- a no-no with the older throttle cable
This cruise control actuator can be disassembled easily.
Remove one bolt at the front end and disconnect the throttle
cable from the disk at the rear end (don't lose the little
cable attachment thingy!) and remove it from the car. Then
peel the bellows away from the disk the cable attaches to,
and away from the solenoid housing the same way.
These units seem to have several common failure modes.
The first and most obvious is that the bellows leaks around
the edges where it snaps over the metal disks; even a small
leak is enough to render the system totally inoperative. If
this problem is suspected, it is a fairly simple matter to
peel the bellows off at both ends, apply some silicone
sealant, and reassemble.
Another common problem is the bellows itself develops a
tear or leak. You can easily check if the rest of the system
is operational by patching the leaks, using a bicycle tire
patch kit, tape, or whatever. It may not last, but it will
tell you if the rest of the system is OK.
It has been suggested that using Son Of A Gun or some
similar substance on the bellows may help protect the rubber
Gregory Andrachuk describes repairing another failure
mode, sticky solenoids: after taking the bellows off, "I
simply lubricated them liberally with Liquid Wrench
(like WD40, but has Teflon). The cruise functioned
Yet another common failure is that the tiny rubber seats
on the solenoid plungers fall off, and the solenoids no
longer seal the ports. To repair this failure, merely glue
the rubber seat back on the end of the plunger. After
removing the bellows, the solenoids can be removed by prying
them out of the housing to get at the plunger. If you've
lost or damaged the rubber seat, use a hole punch on a
bicycle inner tube to make a new one. Make sure the sealing
surface is flat and smooth before reassembly.
It must be pointed out that a failure of a cruise control
could be dangerous, although that would typically require
the two openings to atmosphere to fail closed and the
opening to vacuum to fail open -- highly unlikely. You
should make repairs carefully, using a very reliable glue
(such as JB Weld) to hold the rubber seat on the rod. Use of
unreliable glue such as cyanoacrylate (superglue) is not
CRUISE CONTROL CABLE ATTACHMENT: Bill Trimble
managed to lose the little part that screws onto the end of
the cable to connect it to the bellows unit. "I took the car
over to Rick the Mechanic's to see if he had any ideas, and
sure enough he remembered that one of the local auto parts
places had barrel connectors for hood release and choke
cables. I bought one for a couple of bucks and we fitted it
in about ten minutes, the only modification needed was to
gently pry out the round end on the bellows side to fit the
wider diameter of the new barrel connector. We also wrapped
some safety wire around it so that if the cable slips out
again, the connector won't fall out."
CRUISE CONTROL RELOCATION: To get that bellows
assembly to last longer, it would probably be a good idea to
relocate it somewhere else.(This section seems to be
corrupted -- Vaughan) If you pry the box open, however,
there are two adjustable pots on the circuit board. The one
to adjust is the one in the corner, farthest from where the
wires enter the box. NOTE: The adjuster is very
sensitive; it is difficult to move it a small enough
SERVO/BELLOWS REPLACEMENT: If you have to buy a
new servo unit from Jaguar, be prepared to open your wallet
a long way. You may find better prices if you shop around,
though; Randy Wilson says "Those of us not locked in to the
Jag parts distributing system, i.e. the independents, have
an alternate source for this servos, plus we can get the
bellows as a separate service item. They still aren't cheap,
as they come through a different British car parts network
(RR!), but the servo is about half what Jag wants."
CRUISE CONTROL TROUBLESHOOTING -- WIRING AND SWITCHES:
To check the wiring, disconnect the wiring connectors at
the speed control unit. The speed control unit is located
just under the fuse panel above the passenger footwell. It
has two electrical connectors, a nine pin connector and a
single pin connector. Pull the connectors apart and perform
the following checks on the wires going out to the car, not
to those going into the speed control unit. Make sure that
the bellows unit three wire connector is connected properly
if it was disturbed by previous testing.
Connect one lead of a volt/ohmmeter (VOM) to a convenient
car chassis metallic ground, and test to make sure you have
a good ground using the ohm setting on the meter. The other
meter probe will be used on the pin connectors. Unless
stated, all measurements are made with the ignition
1) Set VOM to ohms and test the black wire; it
should check as zero ohms, since it is a ground wire.
2) The yellow/purple wire is connected to the "inhibit
switch" mounted on the gear selector; this switch opens
to allow the cruise control to work only when the
selector is in D. The same switch serves to allow the
kickdown solenoid in the GM400 transmission to be
activated only when the selector is in D. As a result,
when the selector is not in drive, the wire is not truly
grounded; it is routed through the kickdown solenoid in
the transmission to ground, which is effectively grounded
as far as the sensitive speed control unit is concerned.
With the selector in P (or anywhere other than D), check
that the yellow/purple wire reads low ohmage; it might
not be zero, but it should be low. With the selector in
D, it becomes open; check that it measures infinite
If the console is opened, the physical operation of
this switch can be observed. These type microswitches,
complete with the rollers, are available at electronic
3) The black/pink wire is connected to the set switch
on the turn signal stalk. It normally reads as open
(infinite ohms) but should indicate zero ohms while the
set switch is pushed. See below.
4) The black/slate wire is connected to the master
control switch just behind the selector lever on the
console. It should read open (infinite ohms) when the
switch is in either ON or OFF position and zero ohms when
the switch is moved to RESUME.
5) The yellow/white wire connects to the two bellows
unit solenoids through the brake-operated switch which
acts as a backup to cut out cruise control when brakes
are applied. It should read the 25-30 ohms of the vent
solenoid. When the brake pedal is pressed, it should read
This switch is located on the brake pedal housing
within the engine compartment, right next to the driver's
side bonnet latch. It is threaded into the housing with a
locknut. The locknut can be loosened and the switch
screwed in or out until it works properly.
6) The yellow/black wire is connected to the vacuum
solenoid. It should read 50-60 ohms; this is because both
solenoid coils are in series to ground referenced to this
7) The yellow/orange wire actually connects to two
different pins at the speed control unit connector. It is
connected to the master control switch. Turn the ignition
on, select a suitable voltage scale on the VOM, and check
that this wire reads 12 volts with the switch in the ON
position (center) and zero volts with the switch in the
8) The green/purple wire is connected to the brake
light switch. Normally, this wire should read zero volts;
when the ignition is on and the brake pedal is pressed,
it should read 12 volts.
9) The yellow wire to the single connector is the
signal from the pulse generator mounted on the
transmission. Pulses from this wire signal the cars'
speed to the speed control unit. This pulse signal also
works the speedometer, so if the speedometer is working
it is likely that the pulse is also getting to the speed
control unit. However, the presence of the pulse at this
connector can be checked. Connect a voltmeter to chassis
ground and the connector pin. Drive the car, and even at
very low speed the signal will measure around 4 volts AC.
And the voltage does not increase with speed.
SET SWITCH GROUND: The set switch on the stalk has
a ground wire within the column that connects with other
grounds. This wire has a nasty tendency to break off right
where it attaches to the stalk, rendering the entire cruise
control system inoperative. Any scheme that will provide a
ground wire connection to the stem of the stalk itself will
fix it. The broken wire can be spliced, or a new wire can be
clamped onto the stalk just inside the column housing.
CRUISE CONTROL TROUBLESHOOTING -- SPEED CONTROL UNIT
(IN CAR): If the bellows unit is OK and no problems are
found with the cruise control wiring or switches, the only
remaining component to check is the speed control unit. The
tester shown in Figure
23 is simple to make, requiring only two flashlight
bulbs, two resistors and some wire. It is also used for the
bench test of the speed control unit.
- Length of the three wires is about three
- The two bulbs are 3V flashlight type PR2.
- The 33 and 22 ohm resistors are 1/2 watt or
- The bulbs and resistors are soldered as shown.
- Small alligator clips will help in connecting.
- All components can be purchased from Radio Shack,
Mount this assembly on a piece of cardboard about 4 by 6
Disconnect the connector from the bellows unit and
connect the three wires from this tester to their respective
colors on the wiring harness (not to the bellows unit). The
bulbs and resistors take the place of the two bellows
solenoids so that we can observe the operation of the speed
control unit. Route this assembly out from under the hood
and use a windshield wiper to hold it against the windshield
so you can observe the bulbs while driving.
Next go for a drive. At about 30-40 mph push the "set"
cruise button. The bulb on the left (33 ohm) should light
but rather dimly and stay lit. This bulb is taking the place
of the yellow-white solenoid that closes the bellows to the
The right bulb should light but flicker, and, as you slow
down the bulb will light brighter, and as you speed up it
will grow dimmer. This bulb is taking the place of the
yellow-black solenoid that controls the vacuum from the
If this bulb test circuit works, then the speed control
unit and associated wiring/switches are good. If this test
fails then the speed control unit is possibly at fault.
CRUISE CONTROL TROUBLESHOOTING -- SPEED CONTROL UNIT
(ON BENCH): Bench testing the speed control unit is not
complicated but you do need some experience working with
electronic circuits. Essentially, what we do is connect up
the speed control unit with power and grounds as it would be
in the car, then feed it a pulse generation to simulate
speed and observe its operation with the above two-bulb
tester. Thus, to perform this bench test you will need:
1) 12V battery source
2) about 8 alligator clip leads, mini-size with boots
3) a sine wave frequency generator.
First, fuse the 12v battery supply with a 1 amp
fuse; this will hopefully save you from any nasty smokings.
The speed control unit should only draw around 1/2 amp.
Working with the speed control unit and its associated
nine pin connector make the following connections:
1) Black/red and brown go to battery ground
2) Brown/black is not connected (simulating the inhibit
switch in drive).
3) Brown/white is not connected (used only for "resume
4) Brown/yellow is attached to a clip lead but left open
(it is the "set speed" switch).
5) The two-bulb tester is connected, black to battery
ground, middle wire to yellow/white, and outside wire to
6) Yellow and black/green are connected to positive 12
This completes the basic wiring of the speed control
unit. Next a pulse must be sent into it via the single green
wire connector to simulate the car speed. A simple sine wave
generator that can put out 5 volts at 60 to 200 Hz will
work. The generators' signal lead is connected to the green
wire connector and the ground to battery ground.
With all connections in place and the signal generator
set at 80 Hz, and 5 volts, touch the brown/yellow wire to
ground for a second and remove it. This simulates pushing
the "set speed" switch in the car. The two bulbs should
light with the left one remaining steady while the right one
changes its flickering as the signal generator frequency is
lowered or raised. If not, replace the speed control
CRUISE CONTROL ECU REPAIR: Bruce Segal says, "I've
found that most of the time (except when you really need it)
the cruise ECU's can be repaired by replacing two of the
transistors inside. They are in the lower left hand corner
of the board. The board is arranged so that the wiring
harness comes off the left side. The transistors are
labelled ZTX650 and ZTX750. They can be replaced by Motorola
MPS650 and MPS750. Very easy and very cheap." (Ed. note:
these transistors are nothing fancy, your basic three-legged
items soldered to the board. They are also quite tiny,
you'll need a magnifier to read the numbers on them.)
"The ECU part number is DAC4293. The older part number is
DAC3672. The DAC4293 definitely can be fixed, I don't
remember if the older one uses the same circuit." (Ed. note:
The ECU in my '83 is DAC3134, and contains these same
"By the way the original transistors are Zetex ZTX650 and
ZTX750. Digi-Key (http://www.digi-key.com) sells Zetex so
these parts should be available through them. You can use
ZTX651 and ZTX751 as well.
"The repair only works if the ECU has blown due to its
output being shorted to ground. The output transistors are
very sensitive to any short to ground. I've seen this happen
a lot through the brake cut-off switch. You're right, it
shouldn't happen; if you look at the schematic there's no
connection to ground. We found that if we disconnected the
ECU and measured from the yellow-white wire to ground, we
would sometimes get a low resistance to ground while
operating the brake pedal. The only part we could fault
would be the brake switch. We got into the habit of always
replacing this switch when replacing the ECU. Comebacks went
way down. I never broke apart one of these switches to see
the internal construction. It would be interesting to see
where the problem occurs. Obviously other shorts to ground
can occur at any point along the YW wire up to the actuator.
It's even possible that the actuator has an internal short,
but I don't think that would be intermittent."
The switch that Segal is talking about is the screw-in
switch on the pedal box under the hood, not the lever-type
brake light switch in the footwell.
Note that since the author modified his pedal box in the
course of installing a clutch pedal, this switch for the
cruise control had to go. Not wanting to forgo this safety
feature (this switch positively shuts off power to the servo
when the brakes are applied), a replacement switch was
provided by mounting a standard microswitch within the
footwell so that the pedal itself switched it when fully
released. A microswitch with a long integral lever was used,
which allows the large motion of the pedal to reliably
operate the switch. This installation was very easy to do,
and may be a viable consideration for anyone wishing to
positively avoid the blown transistor problems.
SURGING WITH TURN SIGNALS: The author of this book
may be the only owner who's ever had this problem, but I'll
report on it anyway. Whenever cruising with the cruise
control set and a turn signal was first turned on, the car
would surge forward briefly. Then, after the EFI ECU was
modified to provide better throttle response, the car would
surge on each blink of the turn signals! Once the turn
signal was cancelled, the car would return to its original
set speed -- a clear indication that the problem was not due
to a crossconnection between the set switch and the turn
signal switch, since a "set" signal would cause the car to
increase speed and maintain the increased speed after
the signal is removed.
The problem was eventually traced to a poor connection
providing power to the WK wiring in the car. The WK wires
provide power to fuse 5 and on to the turn signals and also,
via fuse 17, the G wires powering the cruise control system.
The high-resistance connection caused the voltage to
fluctuate more than a volt at fuse 17 when the turn signal
blinked on and off.
In this particular case, the problem turned out to be
within the ignition switch itself; it was pried open and the
contacts cleaned and the problem was cured. Theoretically,
any bad connection along the way would have the same
symptoms, such as corrosion at fuse 5.
SPEED SENSOR: Ron Whiston points out that the
speed sensor for the cars fitted with trip computers is
different than the sensor for cars without computers. The
differences are obvious, the color is different, the plug is
different, but the dealer may still hand you the wrong one.
It's best to take the old one with you when buying a
CRUISE CONTROL REPLACEMENT: Larry Lee sends this
description on how to replace the Jaguar cruise control
system with a generic Dana unit: "The particular unit I
installed was purchased from Sears, Model 318.20309. This
model came with a turn signal lever that can replace an
existing one (if no other switches are on it), but Model
318.20308 included a clamp-on control switch. Other than the
control switch design, the two units are identical. The
manual for this unit does not say "Dana" anywhere in it, but
I recognized the system as very similar to other Dana units
(also purchased from Sears, but marked "Dana Electronic
Speed Control Kit 250-1000") I had installed on other cars
as far back as 1978. There have been some changes over the
years -- such as a change from two driveshaft magnets to
one, and deletion of an inertial deceleration switch -- but
all of them that I have seen are installed essentially the
same way." Note: apparently Sears no longer carries these
units, but they -- or something similar -- may be available
"The installation manual is quite complete and easy to
follow. It includes an electrical schematic and a pictorial
drawing that shows how the various components and cables
connect. The cable plugs are all different, so improper
connections are difficult to make.
Follow the manual instructions to install:
Road Speed Pick-up Coil
Disengagement Switch & Valve Assembly (Brake Switch)
"Some judgment must be exercised when mounting the
The Disengagement Switch & Valve Assembly mounts on
the brake pedal. When the brake is applied, it breaks an
electrical connection to ground, killing the cruise. Besides
that, it also vents vacuum to the system, making doubly sure
it is off. Considering the fact that the stock XJ-S already
has a switch mounted on the brake pedal housing for
disabling the cruise control, it may be tempting to discard
the Dana unit, plug the vacuum dump line, and just connect
the wire to the stock Jaguar switch. Note, however, that the
Jaguar switch works the wrong way; it breaks contact when
the brakes are released, and connects to ground when brakes
are applied. Therefore, a relay would be required to use
this switch. Considering the effort required as well as the
reduction in safety due to lacking the vacuum dump, it's
probably better to simply use the Dana parts.
The driveshaft pickup is normally mounted right behind
the transmission. However, considering how difficult it is
to get around the transmission mount on the XJ-S, it may be
preferable to mount it at the rear end of the driveshaft
adjacent to the differential. If possible, the pickup should
be attached directly to either the transmission or
differential in order to move with them on their soft
mountings; if mounted on the surrounding bodywork, the
transmission or diff -- and hence the drive shaft with
magnets on it -- may move around relative to the pickup,
possibly interfering with the signal.
The Dana kit Lee describes attaches only one magnet to
the drive shaft. While he reports no noticeable balance
effects from attaching the small magnet to one side, those
who are concerned may easily add a dummy weight to the
opposite side when installing.
Note that any cruise control servo should be attached to
the throttle linkage in a similar manner to the original. On
the early XJ-S, it may be helpful to unbolt the throttle
pedal assembly from the firewall and lift it out to look at
it. If the cable connection is relocated to the bellcrank at
the top center of the engine, operation of the cruise
control may cause the throttle cable to come undone or jam;
however, later cars were designed to permit attachment
Locating the servo unit itself may be challenging. The
original mounted just forward of the distributor -- and you
are replacing it, presumably because it didn't survive the
heat in this area. If the cable is long enough, the best
place is probably out in front of the radiator. You could
get creative and make up your own extra-long cable, or find
a way to connect the end of the Dana cable to the end of the
Jaguar cable and use both!
Whichever Dana kit is purchased, the control switch
assembly won't look all that great in the XJ-S interior.
Worse yet, the original set switch (on the turn signal
stalk) and ON/OFF/RESUME switch (on the console) will no
longer be used, leaving either unused switches or gaping
holes where they once were. The following is based on Lee's
method for using the original Jaguar set switch and
ON/OFF/RESUME switch in place of the control switch that
came with the kit. This will maintain the appearance of the
Jaguar interior, but it requires the purchase of a relay.
Note: the illustration shows the terminal layout for an
automotive relay, but any 12V SPDT relay will work. If the
an automotive relay is used, make sure it has the real 87a
connector (normally closed contact). Many standard
automotive relays, notably driving light relays, actually
have two 87 connections and no 87a connections, which won't
work. See the notes on the radiator
Remove the 4-wire plug from the Dana control switch
cable, and connect the Jaguar switches to the plug as shown
24. This sketch shows only the wiring that
differs from the Dana (Sears) schematic in the area of the
control switch; basically, the section of the Dana schematic
from the four-connector plug onward should be replaced with
"How the Jaguar switch functions replace the Dana switch
functions should be clear from the Dana schematic. The
Jaguar switches are physically located in two places, but
that makes no electrical difference. A good ground for the
Set Speed switch is essential (as is a good ground for the
Servo), but it can be located just about anywhere."
For clarity, Lee describes the operation of the Dana
control switch that is being replaced: "It is a single piece
that contains two separate switches, but they share a couple
of wires. (For convenience, I'll refer to the wires by the
numbers shown on the connector.) One is a momentary push
button that is NC across wires 2 and 3. When pressed
(SET/COAST), it opens between 2 and 3 and closes between 2
and 4. Actually, releasing this button is what engages the
control and determines the speed setpoint. The second switch
is a slide switch that has three positions. In OFF, no
connections are closed. In ON, a detented position, wires 1
and 2 are closed. This same switch can be pushed momentarily
(spring return) into RESUME/ACCEL position, which maintains
the 1-2 closure and also closes between 1 and 4."
For those whose parts don't look exactly the same as
those in the illustration, a description of the contacts
made may be helpful. First, the relay: 85 and 86 are the
coil connections, 30/51 is the common contact, 87 is the
normally open contact, and 87a is the normally closed
contact. On the ON/OFF/RESUME switch, placing the switch in
the ON position connects contacts 3 and 7. Pressing the
RESUME maintains the 3-7 connection and momentarily connects
contacts 6 and 8.
"Once the unit is installed, the check-out procedure
described in the manual should be followed without any
changes. Use the electrical schematic to sort out any errors
in the new wiring. Hopefully, this will not be
"The pictorial drawing in my manual showed one
unlabeled adjustment screw on the Regulator." Note:
the adjustment screw referred to here is on the side of the
regulator box, to the left of the "Centering Adjust" screw.
"It should be labeled ëMinimum Speed Adjust.' The
manual describes how to make all set-up adjustments. I set
the Minimum speed at 30 mph, which enables the unit to
maintain a set speed anywhere between about 30 mph and 90
mph. Others may prefer a different range.
"Once everything has been tested and adjusted, push the
Regulator and excess wiring up behind the underscuttle panel
below the steering wheel. I have not found it necessary to
fasten the Regulator to anything.
"One should now be able to enjoy miles of foot-off
Note that while this installation maintains the interior
appearance of the Jag, the Dana cruise control does not work
exactly the same; it has more features. First, the stock
Jaguar set switch is just that, but with this Dana system it
becomes a set/coast switch; if pressed and held when the
system is engaged, the car will slow down, and a new cruise
speed will be set when the button is released. Second, the
resume position on the control switch becomes a
resume/accel; if held down, the car will speed up.
One other issue: The original Jaguar cruise control
system includes a switch on the shifter to ensure that the
car is in D before engaging the cruise control. The Dana
aftermarket cruise control lacks such a safety provision,
probably because there is a built-in electronic control to
prevent the engine from racing if the cruise control is
engaged while in neutral; there is a step in the
instructions for testing the regulator to ensure engine
racing does not occur. The system also supposedly will not
permit engagement below an established minimum speed, so
engaging in neutral would evidently require attaining
highway speed and then moving the shifter to neutral.
If the safety features that are good enough for Dana are
good enough for you, the YP wire from the shifter switch may
be simply abandoned. However, this same switch also ensures
that the car is in D before sending power to the kickdown
switch on the GM400 transmission. Therefore, the switch
itself and the other two wires connected to it -- a LGW wire
to the kickdown switch and a BW wire to the solenoid within
the transmission -- must be left in place for the kickdown
to function properly.
If, on the other hand, you insist upon restoring this
safety lockout, another relay will be required -- a DPDT
this time. A 12V power supply should be fed through the
shifter switch to operate the relay. When in D, one pair of
contacts on the relay should provide the same connection
between the kickdown switch and the transmission solenoid
that was provided before. When in any position other than D,
a totally separate set of contacts should be wired in series
with the disengagement switch on the Dana system.