Classic/Antique Car Repair: 1947 Dodge PU 6 volt electrics, Circuit breaker voltage rating!

Question
QUESTION: My 1947 Dodge PU has its original 6volt system on older restoration including wiring harness. The amp meter works correctly. Problem: When turning on the headlights they come on for a brief moment and then turn off. Without touching anything they will come back on and turn off. This happens with the truck running or not. Have checked for loose connections but no change in symptoms What's wrong?

ANSWER: The circuit breaker in the headlight circuit is cycling - probably it is just worn out and needs to be replaced.

I think on your truck it is mounted on the back of the headlight switch - take a look at the switch and if you see a bathtub shaped thing about 3/4 inch wide, 3/4 inch deep, and 1 1/2 inch long, with two terminals on it, with a heavy wire coming from the ammeter attached to it, that's the circuit breaker.  Unbolt that from the headlight switch and take it to your local NAPA store -or other good auto parts place, they will have a replacement.  Get the 40 amp one, even though you probably have only 25 amp one now - the newer bulbs draw more current.

To work on the headlight switch, it is much easier if you remove it from the dash.  The way to do this is to first disconnect either battery cable, then reach under the dash and feel along the top side of the headlight switch.  You will feel the end of a tiny plunger up there, it is spring loaded upward.  Press down on the plunger - and pull out the switch knob all the way. It should come out in your hand.  Now you can unscrew the bezel around the switch and let the switch hang down by your feet to work on it.

Dick

---------- FOLLOW-UP ----------

QUESTION: Dick
NAPA only has circuit breakers designated 12v. They could not find any 6v breakers in any of their books. Is this going to change the amp draw breaking point of the contact. I bought a 40amp 12v breaker. Is it safe to install this unit to replace the 6v 30amp breaker removed from the system?
Mitch

Answer
A circuit breaker is merely a current limiting device, it doesn't know what voltage it is working on.  Why the store clerk or whoever wrote their parts stock listing thinks it matters, is beyond me to imagine.  The 40 amp breaker is what you need - just install it and everything should be fine.

Dick (With an actual degree in Electrical Engineering!)