Hey there,
I have a question about my car. I have a 1972 Charger that runs well but when night comes around, the car will not idle with the headlights on. The guage lights dim really badly also. The car has been doing this for a while, even after a new alternator. Has anyone experienced this before?

Car specs for ya: 440 wedge, stock ignition, 70 amp oreiley alternator, tight belts, good condition. No big stereo or electric accessories that overload the original system.

Thanks for the input!

 

Do you have a digital multi-meter, or an old analog one that can measure voltage exactly? If you are getting the average 13.2-14 volts at the battery and the voltage regulator output, then it would sound like a resistance problem. "Voltage drop". One major spot to check would be the bulkhead connector for the wiring harness on the firewall. That connection there can heat-up and start melting the connectors there. Turn the lights on with the motor off for a few minutes and feel for excessive heat there. Or unplug it and do a visual, careful, the connectors are brittle. But do the voltage tests first and we'll give you a schematic to go step-by-step with.

 

Sounds like you have some bad grounds somewhere, check for corrosion at the bulkhead connector and all the grounds you can find. Did you paint the motor then install the ground cable to the battery? That seems to be a common thing that a lot of people don't realize they do and spend countless hours chasing nothing more that a coat of paint wreaking havok on the electrical system.

 

I 100% agree. I've seen this done many times over.

 

Awesome, I have a freshly painted engine. I will try that ground first and let you know! Thanks for the help so far!