Re: [xj-s] Alternator Charging, a Quick Fix

[dmeadow@juno.com]

I couldn't find this in The Book.  If it isn't there, it should be.

I've had some trouble keeping batteries charged.  Since I have owned my
'88 XJ-S V12, I have put a new Optima battery in it and replaced the
Lucas 75 amp alternator with a GM 98 amp, thanks to John's Cars GMALT
conversion bracket.

Even with this, I found that my gauge showed "discharge" most of the
time, particularly with the A/C on, although it seemed to get better as
the car warmed up.  For a long time, I ascribed this to just being
another unreliable gauge.

A couple of days ago, my Optima battery was almost flat when I went to
start the car in the morning.  I jump started it and drove it to work
with the A/C off that day (eeeoooww, it is HOT here) and the battery
charged up enough to start it that evening for the trip home.

I checked for a number of the usual items; loose belt, exciter light not
connected or burnt out, an overnight drain.  I found it hard to believe
that the new alternator had gone bad already, as it was charging to some
degree.

That night, the Prince of Darkness came to me in my slumber and whispered
in my ear:  "BAD GROUND, you idiot!".  Of course!  Some of you may have
picked up on the clue above-- charging would improve as the car warmed
up!  As metal parts expanded with heat, the bad ground connection would
get better and improve the flow.  I should have figured this out a long
time ago, given my experience with Lucas on the MG.

Where is the ground?  On my '88 there is a black plastic shield covering
a bracket with some electrical connections on the inside of the passenger
side (LHD) front fender, towards the back of the engine bay.  I removed
that cover and found a couple of ground wires connected to the bracket. 
I cleaned a goodly amount of corrosion off these connections and off the
brass (?) screw that held the bracket to the chassis.

Now, even at idle, the gauge shows "charge,"  even with the A/C on.  I
wish I had figured this out earlier, it might have saved me the cost of a
new battery and a new alternator.  I'm convinced the old alternator died
because of it, and it killed the battery, in turn.

There was no indication that anything was wrong, besides the gauge
reading low.  Those of you that find your battery going flat overnight or
similar symptoms may want to try this fix before removing the alternator.
 Or if you are replacing your alternator, be sure to clean up these
contacts to keep from killing the next one.  Hell, even if neither of the
above is true, you might want to clean up this ground just as a
preventative measure.

David Littlefield
Houston, TX
'62 MGA MkII
'51 MGTD
'88 Jaguar XJ-S


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Follow-Ups:

• Re: [xj-s] Alternator Charging, a Quick Fix
• From: "Kirbert" <palmk@mailer.gadcomm.net>

References:

• [xj-s] Removing the Alternator HELP!!
• From: Jim Isbell <jisbelljr@mail.utexas.edu>

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