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Discussion Starter #1
So i have a 1989 gt covertible. The car doesnt want to charge when the headlights are on. I have checked and repaired the wiring to the alternator, installed a know, good new alternator. The previous owner installed one piece headlights and the wiring to those looks a little questionable. Any thing else i can check? Is there a way the headlights can be wired wrong as to not let it charge? Any help would be appreciated, please. Thank you.

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It is fairly common for the headlight switch to fail, causing enough resistance (heat) to actually melt the switch over time. This can cause an abnormally high load on the charging system.
And, obviously, any other faulty wiring can cause a problem, as well.
 

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Ok. Thank you. I guess i can take a resistance reading on that but i dont think its that because i had the dash out to repaint it when i did the heater core in the car. I did not see any melting on the harnesz or switch but i can check again. Thanks

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Update. I finally pulled the car out and poked around at charging system wiring and found the negative cable to the block loose. Duh!? I let it run awhile and it was at 14v. I shut it off and it sat for a little bit. Restarted it and it wasn't charging as well, like 13.2v - 13v
When i turn on the headligjts the voltmeter is dipping again, down to like 13v. It was fine right after i tightened up the ground wire and when i restarted it now its not! What gives? Any ideas? Thank you.

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Definitely check the grounds. The stock system was never adequate from factory.

When I swapped to a newer 3G unit I had to install new cables and realized how inferior it all was. I also made 2 new ground straps to make sure the system was working correctly.
 

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Discussion Starter #6
Thanks. I might have to do that to this one. I already did the upgrade and wiring on my 93. We will see when i get some time. Thanks again.

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The whole wiring system on the headlights in foxes is completely terrible even when they were new. Many ppl do a full re-wire and put them on a new circuit. You could always do something like how the 94-98 DEPO aftermarket lights do and have an independent harness with relays that bugs directly into the battery and the only factory wiring that is used is the on/off signal wire.
 
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