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Hello, I have a 1942 chevrolet fire engine from the war era and i have not had any problems with this truck until now with my headlights. I am having a problem with the headlights turning off after about 15-20 mins of running. I am assuming that the circuit breaker in the switch is overloading and tripping it out. All headlight wiring is original with the truck, the generator was changed over and it has a leece neville electrical system 6v installed for higher amperage. All in cab original switches are intact and appear to be in good running order. I am looking for ideas on how to check for a short somewhere as it's headlights only. parking lamps are on another circuit. All wiring doesnt appear to have any burn marks or frays under the hood. let me know thanx.

Every circuit in my 38 is fused, no circuit breakers. I don't know about your '42. If it is a wiring issue you'll have a nightmare trying to work with that old cloth covered wire. Any time you touch it the cloth will crumble. If you are having issues with shorts now it'll only get worse. I doubt they would have a harness specifically for your firetruck but YNZ Yesterday's Parts makes very high quality cloth covered harnesses (with OEM markings) and can use your original as a pattern for making a new one. They aren't cheap but you do get what you pay for.

I quick way to try to trouble shoot it is to turn them on for about 5 minutes and start feeling everything for heat starting with the switch,connections and even wires. When lights go out, there is usually resistance and this generates heat. We use a heat probe on a multimeter to chase down problems on over the road trucks.

What happens when you try the upper beams? This may give you a clue.

Check around the dimmer switch for loose or dirty connections, or high resistance contacts in the switch itself. They're bad about developing dirty contacts and making the headlights go dim, or quit altogether.
Jerry

thankyou everyone for your replies. I will check for hot spots tommorrow when i get time. I do know for a fact that their is a circuit breaker inside the switch for the headlamps, and that it's tripping out on some sort of overload after about 15 minutes of lights on. i did not try high beams yet, but they are operational. i am going to do a good overlook of the underside of the dash as well but being the mess that it is, i think i am just going to have to live with turning the switch off and letting the circuit cool and turning them back on again and again. i am actually hoping that it heats up enough for me to see wires starting to smolder. that would cause an ease of repair.

I had a similar problem with my '42 half ton. It had been converted to 12 volts and had an appropriate after market switch. This switch, as well as the original, have a thermal circuit breaker. What happens is the contact gets dirty or corroded and normal use causes heat, which then opens the circuit, until it cools down again. Try cleaning that contact.
I think the heat is right there (don't reach up under the dash and feel for it or you will get a nasty burn).

GoCart879

Run your headlights through a separate relay.
This will provide full power directly from the battery for the lights, and take all the current load off the standard switch and wiring system.

The standard gear will only have to provide a small operating current to activate the relay only.....which will not overheat any of the stock system.

The relay is small and can be hidden easily.

ok, so last night we drove the truck back from our county fair and it is a good 25 miles from our fire station and time wise it takes us like 45 minutes with the truck on the back roads, i drove the entire way with the bright headlights on and they did not go out at all on the roads, just as i pulled into the parking lot of our firehall the lights flipped off on their own, but with me pulling the light switch on 2 or 3 times they came back on for like a minute and were out again until i let the switch cool for a bit. how can i reach up to clean the contacts of this switch without getting burned or a shock? i think the switch is my problem, again no visible burning to any wiring whatsoever we drove 45 mins without a problem.

Try some spray-can electrical contact cleaner that is available at Radio Shack. Generously spray the moving/inside parts of the switch and then rotate and pull-in/pull-out the switch control (I do not know the movement on a '42 switch). Do this several times.

You won't get shocked off 6 or 12 volts. Burnt yes.