Daveinrenton

Friends: When my '87 C4 had head and dash lights that were periodically pulsing (partially dimming), the posts in this Forum pointed to reasons that included bad rectifiers in alternators, bad grounds, and bad headlight switches. I checked and changed them all only to find out that it was none of these issues. Before you make unecessary repairs, consider this reason: worn headlight retractor motors! In these older cars, the original motors can get rusted and worn. In my case, one of the magnets in the driver side headlight motor had broken loose inside the housing causing the whole mechanism to slip every 7-10seconds (like the motor did not think it was fully open or closed). The passenger side had worn teeth in the motor gears causing it to similarly slip. Everytime the motor engaged by slipping internally, it caused a quick draw of power from the battery causing the lights to dim for a second (like a half-blink). I started by replacing the motor gears and trying to re-attach the loose magnet. This was the high labor, cheaper parts attempt to fix the issue. This was only partially successful since the driver side motors was rusted and beyond repair. The passenger side worked because the magnet was still intact. I ultimately had to replaced the motors (unfortunately at considerable cost but I kept the rebuilt passenger unit for a back-up) but it got rid of the problem. I also have a new alternator and light switch that I did not need! So, if you have periodically half-blinking head and instrument lights and before replacing alternators and switches and wires and grounds, do this test:

1) Lift hood
2) With engine off, turn on the headlights
3) Observe the engine compartment and listen for periodic noise from the headlight motors.
4) If you do not hear a periodic electric motor noise or see the lights half-wink, your issue is not the headlight motors and you can proceed to the other possibilities mentioned above.

Dave

Lemme

Glad you found the problem. Observe, listen, smell. Then run some tests. All these things can give a clue.

I had an alternator that wouldn't charge after purchasing the vette secondhand. Like you I bought a new alternator only to find it still didn't charge. The problem turned out that somebody had altered the wiring to the charge light and the dash overlay so that it was never going to work.

jfb

When you repair automobiles or anything else, you have to keep your mind totally open and thinking of possible causes and devise experiments to prove your theories.
People who alter wiring and don't keep a record of it should be stoned to death!!

Ray Quayle

Couldn't agree more!