Weird Generator light issues on '68 - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 02-07-2014, 06:39 AM Thread Starter
 
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Weird Generator light issues on '68

Okay guys I'm slowly but surly working through my new '68's gremlins and now I'm down to the electrical system. I have a strange issue going on with my Generator light. With the car running normally the light is on very dim, it really cant be seen during the day, but at night it is visible on the dash. The light does not change in brightness when I turn on headlight or other electrical items. So here is where it gets strange - when I put on the emergency brake the Gen light comes on full bright and goes back to very dim when I release the brake. Here's the REALLY strange part - when I hammer down on the gas, the light goes full bright and then back to dim during normal driving. The car is 100% stock and no one has messed with the wiring to my knowledge.

I checked the alternator and its putting out high 13v to low 14v and compensates when I turn on or off electrical items. Even though it seemed the OLD voltage regulator was working I replaced it with the Ames solid-state regulator and nothing changed.

Id sure appreciate any help with this one fellas. Thanks!
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post #2 of 6 (permalink) Old 02-07-2014, 08:52 AM
 
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The only thing that I can tell you is, after dealing with electrical gremlins of my own in my 67 Le Mans is that your going to have to check EVERY ground connection, everywhere! to be sure the grounds are good and tight and clean. I would venture a guess that that is the most likely culprit in this case, as in most cases. Check the engine ground to chassis especially, dash grounds etc... Good luck working it out.
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post #3 of 6 (permalink) Old 02-07-2014, 09:17 AM
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Smile... sounds eerily similar (though not identical) to a problem I had with my car. Go through and check all your fuses, especially the ones that feed the instrument panel lights. The circuit for the GEN light is weird. It actually sees voltage from two sources in two different directions. One is from the alternator output, the other is from the battery via the instrument light circuit. It's set up so that if voltage is present on "both sides" they cancel each other out, no current flows, and the light is off. When it's on, what's actually happening is that it's seeing voltage on only one side - which causes current flow - and turns on the light. If the instrument light fuse is blown, your instrument lights will still work as long as the engine is running because they'll get power from 'the other direction' via the alternator output. On automatic transmission cars, the TH400 kickdown switch is in the same current path. Turns out that what was causing that fuse to keep blowing on my car was a frayed wire on the kickdown switch connector on the transmission that was shorting out occasionally under hard acceleration --- not that I'd ever do that

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post #4 of 6 (permalink) Old 02-07-2014, 12:26 PM
 
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I had pretty much the same problem, in my case it was a bad voltage regulator. Will your car stay running if you disconnect the battery?
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post #5 of 6 (permalink) Old 02-07-2014, 10:48 PM Thread Starter
 
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Thanks guys! Bear, what a crazy system that is! I would have never figured that out, I will check everything under the dash first thing in the morning. NoGoat, I just changed the regulator from the original to a new "solid state" and same problem.
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post #6 of 6 (permalink) Old 02-08-2014, 01:28 PM Thread Starter
 
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Quote:
Originally Posted by BearGFR View Post
If the instrument light fuse is blown, your instrument lights will still work as long as the engine is running because they'll get power from 'the other direction' via the alternator output. On automatic transmission cars, the TH400 kickdown switch is in the same current path. Turns out that what was causing that fuse to keep blowing on my car was a frayed wire on the kickdown switch connector on the transmission that was shorting out occasionally under hard acceleration --- not that I'd ever do that

Bear

Bear, Ill be dammed if that wasn't the problem! The fuse was blown and I never thought about checking it because my dash lights worked just fine. Ive been having problems with the gas gauge too and now it works perfect! I also couldn't figure out why the kickdown wasn't working either, well guess what? It works now too! Im so stoked, that fuse took care of all the seemingly unrelated electrical problems I was having. Now everything all works perfect! Thanks!!!
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