I've been away from the forum for a while and I missed it so here is my latest issue for you guys to help me with. When I pull the headlight switch in my '65 F250, the lights come on OK for a couple of seconds and then they go dim and then bright and keep alternating like that. When they go dim, the ammeter needle pegs to the discharge side and the gauge clicks. If I do not turn on the lights, the truck starts and runs fine with no fluctuation of the ammeter needle. Sound familiar to anyone? I replaced the headlight switch and then the regulator because I had good ones on the shelf but they did not make any difference. Thanks, Steve

 

It could be in your dimmer switch or the wiring going to it.

 

Have you checked the alternator? It may be getting weak under the load of the headlights.

 

The dome light and the dash lights dim at the same time so I ruled out the dimmer switch. I will have the alternator checked out. Thanks, Steve

 

Regulator? I like the Delco 12SI one wire deal. Or the newer Ford 3G.

 

I could be entirely wrong, but what I think you're describing is a dead short in the headlight circuit (chaffed or trapped wire?) that is causing the circuit breaker built into your light switch to cycle. Short circuits will cause the amp meter to go to full discharge. Hope you find your problem.

 

I would do the same and also ck amp gage circuit then all the grounds starting with the light circuit

 

Just curious...Do the lights dim if the engine is off? Is the vibration of the motor causing enough movement of the headlight wires to short to ground? Wiggle them with engine off. Do they dim then?

 

X2

The problem appears to be in the headlight circuit. The pulsating of the lights is most likely the circuit breaker reacting to a short circuit or a fault to ground.

I would focus on the headlight circuit since you say the rest of the appears to work as normal.

Good luck.

Roger Carter

 

Check the ground wires coming from the Headlight assembly to the Radiator support... Mine did that and it was just loose ground wires...