My 65 with an alternator randomly headlights randomly dim completely. I have replaced the headlight switch but that didn't solve the problem. I also finally replaced my battery (which lasted 6 years). Whenever it feels like it, the headlights will cut off and even though the instrument gauges still work well. I am looking for a ground wire problem as right now, shutting the doors firmly seems to restore things for a while. I have heard that Haologens overtask the breaker in the switch, the cars acts the same no matter what head light switch I have in the car.

Any suggestions?

 

sounds like a ground issue, also make sure you light bulb are properly inserted and are not moving around.

 

Classic symptom of overloaded headlight circuit breaker. As they age, they can't take as much power draw. I have halogens, and they are OK. You could try a 69 switch, that was for 4 light system.

 

Relays are wonderful solution to high draw/inadequate circuit situations...

 

There is actually a plug-in relay harness setup for high-power headlights in older Mustangs.

 

I set up my headlight switch to control a relay that switches the headlights. Ended my headlight problems.

 

I also think that running relays is a great idea with Halogens. It can also make the lights brighter since more voltage reaches the lights.

I am using this relay setup. I am very happy with it.

http://rjminjectiontech.com/products/headlight-harness

 

yep. that's the one. on my to do list as well

 

So loosed and re-tightened the headlight grounds and redrilled the cylinder head to firewall ground. Problem occurred around the same places on my commute. I never thought of this before, but I forgot to check the the floor mounted high/low beam switch.

 

That switch, like all others, can corrode with age and increase the resistance in the circuit. The wires leading up to the switch can also corrode, so check those too.