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Re: [Tigers] Electrical Gremlins

To: Richard Bruner <gammaman@mokancomm.net>
Subject: Re: [Tigers] Electrical Gremlins
From: Theo Smit <tsmit@shaw.ca>
Date: Sun, 09 Sep 2007 09:41:12 -0600
Hi Richard,
When things suddenly all start to go bad in the electrical system, it's 
usually because one of the grounds has become disconnected. You should 
check the cable between the engine and the chassis (usually attached 
between the bellhousing and the chassis at the Alpine transmission 
crossmember mount) as well as the smaller grounds that attach to the 
generator housing. The car running regardless of the ignition can also 
be caused by a bad ground although it's not immediately obvious to me 
how... The dash lights are grounded via the instrument cases, which are 
grounded via the daisy-chain wires... but if those come loose, then the 
dash lights would ground through the instrument temperature sender. This 
would change the way the gauges worked depending on whether or not your 
lights are on.

The parking lights turning on when  you depress the brake pedal is 
definitely a bad ground in the tailllight/brakelight circuit. When the 
brakelight/taillight bulb case isn't grounded, applying  12 volts to the 
brake light causes current to flow through the brake light filament, 
then through the taillight filament in the same bulb, and from there to 
the parking light filament (which is on the same circuit as the 
taillight), and thereby illuminate all three. If you then turn on the 
parking lights, you supply 12 volts to the taillight circuit which would 
then cause the brake light and taillight to go out!

You're going to have to go through a lot of your car with alligator 
clips and test lights (or a voltmeter). A problem with bad grounds 
(especially the main engine/chassis cable) is that starting the engine 
will cause high current to flow through all other possible ground paths 
and that can wreck a lot of stuff. Been there, done that.

If you have any more specific symptoms I can try to make sense of them 
for you if it will help localize the issues.
Good luck,
Theo
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