Both Headlights Popped

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72Duster440

72Duster440

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A few years ago I retired my entire car with a Painless wiring harness and for the headlights I used a standalone harness from Crackedback. Every thing has been working great for the last 4 years, fast forward to a couple days ago... I started the car after it’s been sitting for a few months, turned on my headlights, backed out into the street and put it in drive, the second I hit the gas pedal, both headlights blew out the filaments. I switched to high beams so I could have some light, and the same thing happened, both bulbs popped.

I got back home and everything seems to be functioning as intended, the fuses are good, the relays work when they are supposed to and with the car off I get 12.4 volts at the headlight plugs. The only thing I can think of is that I have the standalone harness hooked right to my alternator, and maybe from the car sitting the regulator upped the voltage to charge the battery and it put out enough to overvoltage the bulbs to pop them? They were the GE Nighthawk sealed beams for reference.

Any ideas? Does my thought sound viable?
 
Yep. Do you have a volt meter or ammeter? What did it show when you started the car? I had a bad regulator ground that did the same thing. It overcharged to 17v. and burned out the headlights, and a few other bulbs.
 
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I do have a volt gauge, but I wasn’t looking at it at the time. I’m just glad it didn’t take out my EFI. I’ll make sure the regulator mount is clean, it grounds through the bolt right?
 
72Duster440 said:
I do have a volt gauge, but I wasn’t looking at it at the time. I’m just glad it didn’t take out my EFI. I’ll make sure the regulator mount is clean, it grounds through the bolt right?
Click to expand...
Yep.
 
Did you have to jump start it? Letting the altnerator charge the battery can be a bad thing.
 
toolmanmike said:
Yep. Do you have a volt meter or ammeter? What did it show when you started the car? I had a bad regulator ground that did the same thing. Ivercharge to 17v. and burned out the headlights, and a few other bulbs.
Click to expand...

I was planning on posting it till I saw you did.:D
Good call.
 
If the alternator is for some reason going over-voltage, you can usually "regulate" it by modulating the engine RPM. Start the car trying not to use too much RPM. Monitor voltage AT THE battery and gently bring up RPM. If it climbs much above 15--15.5 you have a big problem.

Alternatively, monitor right at the alternator stud. A wiring error.........or wiring failure..........might be allowing that terminal to go quite high even though the battery is somewhat "normal." If you have loads off that point, rather than at the battery, the loads will then "see" that higher voltage.

An example of this is a factory stock Mopar with the "usual damage" to the bulkhead terminals and or ammeter. The voltage drop between the alternator output terminal and the battery could be several volts. Some people advocate taking loads off the alternator output termninal, an example might be big driving lights. So if there is a problem in the harness, the alternator terminal will run quite high and supply those lights with too much voltage
 
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