The Stovebolt Site Forums The Shop Area The Electrical Bay Light switch 12v conversion

I am converting from 6V to 12V on my 1949 3600. The kit from vintage auto garage included a relay for the headlights. Is this necessary? I have read many threads on 12 V conversions and have never seen a reference to a relay for the headlights. The instructions said it might be necessary because of the “increased amperage” going through the headlight switch. But there should be FEWER amps going thru the headlight switch with 12 V, correct? If the relay is necessary I will install it but would prefer not to.

Also, I wired the voltage reducer for the fuel gauge by inserting it midway in the powerline going to the fuel gauge. Was much easier than trying to reach under the dash and install the voltage reducer on the gauge itself. I grounded the reducer and isolated it from any metal to metal contact on the dash. Is there any reason this won’t work? Seems to me the gauge won’t know or care where the reducer is located. Thanks so much for all your help don’t know what I would do without your collective expertise. Tim

For the most part switches don't care about voltage. They care about amperage so you're correct with that assumption. If the wattage is the same, a 12v circuit will draw half the amps of a 6v. If the 12v headlights are rated a higher wattage it may make a difference but it would have to be a lot higher I would think. If I'm wrong someone will point it out.

There wouldn't be a need for a relay, since if you use the original 6V wiring, it'll probably be larger gauge than a newer 12V harness. Smaller wire increases voltage drop, and would be the only reason you'd need a relay for the headlights, which reduces voltage drop thru the switch contacts (actually eliminates the switch in the actual light circuit).

Theoretically your voltage reducer should work anywhere in the circuit.

Should not be a problem. I've done this a few times and have never had any difficulty with switches. Gauges, motors, radios...things like that will be sensitive to 12v, though. Your fuel gauge should not care as long as the voltage to it is reduced to 6v.

A relay for the headlights isn't a bad idea at all, but generally I've not found it to be necessary. However, in honesty a relay will keep your headlight switch from wearing out as fast. A month or two I showed what had happened to a headlight switch over years of use and how to make it work like new again. Don't forget your dash lights and hi-beam indicator light. Also your interior light above the seat. If they're 6v, they need to be changed to 12v. Good luck, Tim. Sounds like you have a pretty good understanding of this.

Thank you all – it is so helpful to have guys like you to bounce ideas off of, I greatly appreciate you pitching in!

Keep the relay on the shelf incase you decide to up grade the head lights to a high amp brighter version at some point. I needed to install one on my little cobra when I up graded the bulbs and my 60's vintage switch did not like the higher amperage. Was driving along with lights on and the switch evidently got hot and started breaking contact. Not good on a dark back country road.

Hey guys, finally finished up my 12 V conversion project. Installed the battery today fired it up and everything worked perfectly! I was surprised at how quickly a 6 V foot stomp starter turns over with a 12 V system. Truck fired up immediately. No problems with the fuel gauge if you recall I inserted the reducer halfway in the line instead of fiddling with the almost impossible to reach gauge under the dash. Also, my ammeter is rock steady, with the old generator it used to bounce around a little bit. Now, after starting it naturally moved to the charge side and steadily returned to neutral, I couldn’t be happier. My turn signal and parking lights are much brighter and my halogen headlights are awesome! Thanks for your advice and confidence. By the way, if I can do this, anyone can. I am the classic shade tree mechanic learning one step at a time. Love Stovebolt and my old 49.
P.S. Jon G I found your thread about rebuilding the headlight switch, very cool. I’m sure someday I will have to do that. Now I know how! Didn’t look too terribly difficult.