I bought an old aftermarket light switch on e-Bay for a few dollars. Mostly because it was new, cheap, and looked good. However, I completely over looked the fact that it didn't say if it was 6 or 12 volt. If I had to estimate how old it was, I'd probably say 1950's or early 1960's because the address of the manufacturer has a postal zone number rather than a zip code. If anyone may know anything about the manufacturer, the light switch is made by Joseph Pollak Corp. and the part number is 1605.
The switch won't care what the voltage is. As long as it is rated for the correct amperage you should be good to go.
I am using all the original switches on my 37 chevy p/u and 55 ford with 12 volts and no problems yet. Jeff
12V SHOULD be less current than the old 6 Volt systems, so if its an older switch it should be good to go.
If it is originally designed for a 6V system, it will work fine (12V systems typically have less amperage). If it was originally designed for 12V, it should work fine on that voltage, but might (key word might) be marginal for use with a 6V system. In either case, make sure you don't have too many killer (modern) lights hooked up to it; those super bright bulbs use some power.
Ohms Law I=V/R I= Amps V= Volts R= resistance If you know any two values you can find the unknown. Don't want to come across as a know it all but As said above 6 volt systems draw more amperage because they use less voltage (pressure) to do the job. How you figure out what the circuts resistance is, Volts times amps = Watts. So a ten amp 12 volt circut or switch will run two 600 wat headlamps.
Wouldn't worry about it. It's amperage that matters. If it was designed for a 6v system it will hold up to a 12v system no trouble.