I'm in the process of rewiring my 52 F-1 and encountered this problem. The battery is an 8-volt unit. I finished all of the wiring and tested all of the lights. They work but the new (6-volt) headlights that I put in are both burned out after only being on for about a minute. I am just trying to confirm my suspicions here. The truck ran when I bought it but needed work. The previous owner had 12 volt headlamps in it but the wires were cut off. He did change the front grill and I thought he may have stuck the 12 volt ones in just to fill the holes. Now I'm thinking he had 12-volt lamps in because of the 8 volt battery and was burning the 6-volt lamps out. This is kinda like "well dah" math here but powering 6-volt lamps with 8-volts isn't good, that's 33% more than the rated voltage and I think even 10% over is pushing it. On the other hand, powering 12-volt lamps with 8-volts is a 33% drop and even though they wouldn't very bright, at least they would work. Does this make sense or were 8-volt batteries a norm? I'd think that with 33% more voltage, I'm putting way too voltage on not only the lamps but the gauges, voltage regulator, capacitor and sensors as well.
Thanks,
Jeff