Re: [xj-s] Alternator repaired/more on "extra" connector

[Mike Morrin <mikem@southern.co.nz>]

At 21:14 16/07/98 -0700, Sean Straw wrote:
>At 09:57 15-07-98 -0500, Jim Isbell wrote:
>
>
>On my '88, I've measured resistance between the battery post and frame
>ground (three points - a tiny unpainted exposure on the fuel tank, the
>ground strap itself (at frame), and one of the ECU mounting/ground bolts -
>I get .9-1.0 ohm resistance (might need to do a scrub on the post or
>something, but overall, this seems fairly trivial resistance).  

If that were an accurate reading, it would be far from trivial, as at 10
amps, there would be 10 volts dropped across the circuit.  It is likely
however that your measuring tools are inappropriate.

To measure the resistance of wiring or grounds on a car, you must either
use a 4 wire measurement technique, where the measuring current does not
flow through the same test leads as the voltage sense.  The easiest way to
use your digital meter for this is to get a known load of a few amps
(perhaps a headlamp bulb) and run that via the circuit or ground you wish
to test, and then use your digital meter to measure the VOLTAGE drop across
the circuit under test.  Apply Ohms law (Ohms = Volts/Amps) and threr you are.

Any circuit which carries starter current should have resistance less than
0.0005 Ohms, any circuit which powers your headlights should hve resistance
less than 0.005 Ohms etc. etc.

regards,

Mike Morrin
'75 XJ-S
'73 E-type

---

References:

• [xj-s] Alternator repaired/more on "extra" connector
• From: Jim Isbell <jisbelljr@mail.utexas.edu>
• Re: [xj-s] Alternator repaired/more on "extra" connector
• From: sean.straw+Jaguar@mail.professional.org (Sean Straw)

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