1972 442 head lights dim

[1972 X code 442]

Yes, at first I thought it was a diode in the alternator gone bad. I had the alternator checked out by a good local shop and they said that everything was fine.

I'll check the corrosion / proper ground stuff first. I will let you know what I ultimately find is the culprit.


When I apply the brakes the headlights and dash board lights dim slightly. When I release the brakes the headlights and dash lights brighten up again. Has anyone experienced this and what was the fix? I'm thinking it's a voltage regulator internal problem. With the engine running and using a volt meter the voltage drops to about 12.5 volts when the headlights turn on and then goes right back up to 14.5 volts.

Help!!

[Lady72nRob71]

Welcome to Classic Olds!
Where are you measuring the voltage at? That can help diagnose the problem...
Yea, the reg or alt could be suspect, especially if you are measuring at the battery posts.
Does turning on the heater fan, wipers, or defroster do the same thing?
I assume you have stock bulbs in the brake lights (which draw about 7.5 amps total)...

If voltage looks okay at the battery posts, there could be bad connections, breaking wiring, or improper wire gauges in wiring that had been replaced. Let us know what you find...

[joe_padavano]

Originally Posted by 1972 X code 442

When I apply the brakes the headlights and dash board lights dim slightly. When I release the brakes the headlights and dash lights brighten up again. Has anyone experienced this and what was the fix? I'm thinking it's a voltage regulator internal problem. With the engine running and using a volt meter the voltage drops to about 12.5 volts when the headlights turn on and then goes right back up to 14.5 volts.

Help!!

I had this happen once and it turned out to be corrosion on the terminals at the threaded post on the horn relay. Your problem could be corrosion in contacts almost anywhere. Check the terminal on the alternator, terminal on the horn relay, grounds for the headlights, grounds for the dash lights, etc. I'd also check the brushes in the alternator. I had that problem with my 86.