Headlights start to flash after about 5 minutes--help please!

[ramiedigger]

First time posting!  Just got a couple 1970 Challengers and the 'nicer' one has a couple electrical issues.  The headlights, both low and high beams, work just fine until they have been on for about 5 minutes.  Then they start turning off and on in 3-5 second intervals.  If I turn the switch off and wait a while then turn back on, they will stay on for a while before the flashing occurs.  So it is something with the heat.  I had this issue on a Ford 15 years ago and remembered that changing out the foot dimmer switch fixed it.  Pulled the dimmer off the other Chally and put on this car but had the same result.

What is 'overheating' on me?  I don't hear any noises in or out of the vehicle (with engine off) if that helps the diagnosis.

Oh, all other tail lights, side markers, etc work just fine and do NOT turn off and on.  It is only the headlights.

[Chryco Psycho]

could be a bad switch , are you sure the headlights are stock wattage ?
 using 2 relays will remove the load from the switch & brighten the headlights too , good upgrade , most newer cars use a headlight relay system 

[ramiedigger]

could be a bad switch , are you sure the headlights are stock wattage ?
 using 2 relays will remove the load from the switch & brighten the headlights too , good upgrade , most newer cars use a headlight relay system 

Thanks Chryco (used your key removal trick of rotating the steering column 30 min ago--thanks!)
I will check the headlights but they do appear to be stock wattage.  How would I check to see if the switch is bad?  I have seen a guy listed on the forum that fixes them but I would like to make sure it is broken first!

I am also trying to keep the car as 'stock' as possible seeing that it is a numbers matching r/t so not adding additional aftermarket items would be preferred (although is sounds like a 2nd relay would be a great fix).

[Chryco Psycho]

I would contact Jim / Slotts about the switch he repairs them & my bet is that is where the problem is .

[Haddixj]

Chryco any info about how and where you mounted the relays?

[Chryco Psycho]

close to the start relay works , I hid mine in front of the rad wall under the fender lip & shunted power from the start relay battery terminal

[MEK-Dangerfield]

This is a toughie. I have never seen an intermittent headlight switch before.

Having said that, if both sides are going out at the same time, and all side makers lights and tail lights stay on, the switch is the only thing it can be. Apparently that one contact for the headlights has eroded, but not  completely. 

[73EStroker]

Also sounds like someone may have installed one of those self resetting thermal circuit breakers and it trips first then cools down and resets. Wiring is so ugly on most of these cars as they have been butchered and bastardized by every wannabe mechanic over the last 40 years. I simply replaced everything, with stock used or new replacement harnesses, that looked suspicious or had been spliced and so far no issues.

[dodj]

Switch needs to be replaced, unless what estroker suggested is true. I believe there is a self reseting contact in the stock switch.

[ChallengerHK]

Switch needs to be replaced, unless what estroker suggested is true. I believe there is a self reseting contact in the stock switch.

I'll bet this is it exactly. My Javelin used to do the same thing. Instead of the switch being bad, though, it was doing what it was supposed to do. I found a bare wire hanging from the tag light which was making intermittent contact with the bumper and tripping the breaker in the switch.

[ShelbyDogg]

There is a circuit breaker built into the switch like stated above.  When I changed my headlights to H4 bulbs, my headlights would click off after a few seconds, when using my brights. Not fun when you are driving and your headlights turn off. Luckily, Chrysler put a self-resetting circuit breaker into the switch so the light come back on after a few seconds.  I installed headlight relays on all of my cars. It saves the switches and the lights are brighter.

Mounted above my starter relay with their own separate circuit breakers for highs and lows. The small fuses protect the power circuit to the relays. You can tap right into the harness anywhere between the switch and headlights.

[duodec]

There's a good article and schematic for the headlight relay upgrade at Daniel Stern Lighting