High beams flashing

Hi, I have a 1970 GS 455 and noticed a problem while driving the other night. I switched my headlights to high beam and they worked fine for about 30 seconds. Then they started to flash on and off like 4 way flashers. I switched them back to low beams and they stopped flashing. Switched back to high and they started flashing again after about 30 seconds. Anyone have any ideas what the problem could be?

Thanks

 

Someone probably installed an old JCWhitney headlight flasher thinking it was cool back in the day, or you have an old volunteer firefighter's car similarly modified.

Devon

 

Has it happened before?
Was it very rhythmical?

 

There is a "Thermo Circuit Breaker" in the headlight switch, which will cause the headlights to flash when there is a short circuit. So either you have a heavy draw somewhere, a cut wire, or the headlight switch is bad.

 

Thanks Dean. i'll check it out and let you know what I find. Rock

 

No, but i've only owned it a few months and don't drive it much at night. It was rythmical just like 4 way flashers. Both beams go on and off, but the low beams work fine Rock.

 

Hi Devon, Yeah I'm not sure what it is, but checking the flasher is probably a good place to start. There were a few more ideas posted after yours. Guess I'll try them all!

Thanks again, Rock

 

Could also be caused by an intermittant filamant short in the high beam lamp. That's what caused this in my 65.

 

I like Dean's info. I've not heard of that before, so check it out.

Devon

 

It's in the lighting diagnostics section of the chassis manual.

 

My flashing was caused by the thermo breaker going on & off. The cause for it to trip was the intermittant short in the headlamp filiment.

 

Thanks Dean. I'll try that next. So I should probably just change out both high beam lamps to be safe?

Thanks

 

Headlamps should always be changed in pairs anyway. Especially when they are very old.

Rufus

 

If it's the thermal breaker in the switch you might gain some insight by this trick (it worked for me). Simply disconnect ONE of the high beam lamps and see if it works OK on high beam for just three lamps. If it does disconnect the other and reconnect the one just disconnected. If it works OK again it is almost assuredly the thermal breaker (especially if you have the original headlight switch).

 

Hi, I tried your trouble shooting technique for determining if the thermal breaker was bad and you were right. They did not flash on and off when the headlamps were disconnected one at a time. I boughht a new headlight switch, but it looks like a bear to get at. Any tips on removal and installation of the new one before I start tearing into it?

Thanks, Divecop

 

Well I guess I have a heavy draw/short somewhere. I just replaced the headlight switch, the high beam bulbs and the foot dimmer switch and nothing. In fact, now they blink on low beams too! I give up...

 

Well I guess I have a heavy draw/short somewhere. I just replaced the headlight switch, the high beam bulbs and the foot dimmer switch and nothing. In fact, now they blink on low beams too! I give up...<!-- / message -->

 

Well I guess I have a heavy draw/short somewhere. I just replaced the headlight switch, the high beam bulbs and the foot dimmer switch and nothing. In fact, now they blink on low beams too! I give up...<!-- / message -->

 

Interesting thread, my high beams flash exactly as you describe. As of yet (2 years) I havn't been able to fix it. The funny thing with mine is the headlight motor is buzzing in time to the lights...

 

I have been thinking about this problem a bit and what I would do if I were faced with it.

I think this is what I would likely do to narrow down the problem.

1. I would run power directly to the power side of the headlights with a jumper wire. This would tell me if it was a ground issue by eliminating the power side variables
2. If that did not show it to be a ground problem, I would unplug the headlight switch and run a full power jumper to the power wire that goes from the switch to the headlights. If this makes the headlight work properly, then you know that the wiring from the switch to the headlights is not the problem.
3. If the headlights work properly with the previous test, I would plug the switch back in and run a jumper to the main power in plug of the headlight switch and test the system. If the headlights still work properly, you know it is in the wiring between the fuse box and the switch.

This is how I would chase the problem. I would not recommend this type of diagnoses on a late model-computer controlled cars, but I would feel comfortable doing it on our old cars.

Also, a web search turned up this thread on a Chevelle with a similar problem.
http://www.chevelles.com/forums/archive/index.php/t-55571.html