Headlights cycling on and off, 1950 Plymouth

[rhelm1953]

Driving home last night my headlights and dash lights started cycling on and off.  Once I got home I left the car running in the driveway and the lights would come on for about 10 - 15 seconds and then go off for about 5 seconds and repeat the cycle.  High beam, low beam didn't matter.  I have just replaced the dimmer switch (low beam quit working) and I have wired in an overdrive relay according to the factory schematic.  Overall the wiring is in good shape and it looks like the harness may have been replaced a few years ago.

 

Has anyone else had this problem?  Is there a circuit breaker in the headlight circuit that could be cycling?  If there is a circuit breaker where is it and can I replace it with a 20A fuse?

 

Until I have answers I'm not driving at night!

 

Rich

[ptwothree]

There is a short curcuit that you need to address.  Old wiring perhaps?  That breaker is all that is keeping your car from burning down.

 

That breaker is trying to tell you something.

[mopar_earl]

There is a short. Find your short. The short is causing the automatic circuit breaker to trip. Putting a fuse in isn't safe or legal in my state and won't fix the issue. You will just keep blowing the fuse.

If it doesn't do with with the parking lights on only, than short is in the headlight circuits.

Earl

[Mark D]

I had this issue and it turned out to be a worn out head light switch.  Took the switch out, took it apart, cleaned it and put it back together.  Been working fine since.

[Niel Hoback]

Fix the short before you lose your shorts!

[dpollo]

Look for a light that is not working.... like the license plate light or a tail light. That will be a good indicator of where the short is.

[Branded]

If I'm reading this correctly, the issue started after replacing the dimmer switch. If that's the case either you have a defective switch or you have a short.

[Pete]

Hi, I had something similar when I replaced the dimmer switch in my 1938 DB pickup. The switch was a repro and a bit wider than the original. Whenever I push the clutch in it touched a contact on the dimmer switch and blew the fuse in the Auto-Lite headlight relay I put in. A good wrapping of electrical tape on the dimmer switch solved the problem.

Pete

[Don Coatney]

Last thing worked on (dimmer switch) is the first place to look.

[Dan Hiebert]

Check your grounds and connections as well.  Bad ground, or loose connection, can have same affect on electrical system as a short. 

[rhelm1953]

Thanks for all the replies, I hate trying to track down shorts so I was hoping the circuit was a known weak link.  Apparently not...

Don, my basic trouble shooting procedure is to start with what I worked on last.  It's a sometimes humbling exercise but quite often very effective. 

Guess I will be spending some quality time with my Ohm meter and test light.

[TodFitch]

Thanks for all the replies, I hate trying to track down shorts so I was hoping the circuit was a known weak link.  . . . Guess I will be spending some quality time with my Ohm meter and test light.

 

At least the vehicles of the 40s and earlier have very simple wiring and much of it pretty easy to get to. When my '82 Plymouth developed electrical issues when it was 8 or 9 years old it was a real pain to isolate it to some badly crimped pins on a bulkhead connector and I had to disassemble what seemed like half the engine compartment and front passenger are to get to it.

[greg g]

You can power the headlamps by using a jumper wire from the battery to the connection block near the radiator.  If they work normally, you know the circuit is ok from the junction block to the lights. You can then power the dimmer out erminals, then the dimmer switch with the jumper, and then you will know that the circuit from the dimmer to the lights is OK. That then leaves the fault either within the dimmer or from the switch to the dimmer.You can power the wire from the switch out  terminal through the dimmer, and that will eliminate that portion of the circuit.  Leaving the switch or the power to the switch.

[Merle Coggins]

The test that Greg outlines are good troubleshooting steps. However, I would also add a fuse, or circuit breaker, in with your jumper wire so if/when you find a short you won't let the smoke out of all the wires.

And that brings up another thought... Maybe your circuit breaker is just getting weak and tripping too early.

Merle