It sounds like someone threw a 12v battery in there without knowing what he/she was doing.
There will be a number printed on the backs of your headlight bulbs. If that number is 6006, then you have 6v bulbs. I'm not sure what the 12v number is on a 7" sealed beam light.
What color is the tag on your generator?
If it's black and silver, then it's probably a 6v.
If it's red and silver, then it's probably a 12v.
Also, look at your starter. Same color rules apply.
The starter will work fine on 12v if it's a 6v. The generator and regulator, otoh, don't work on 6v.
Have a peek at your coil. Is it a 6v or a 12v coil?
If you do have a 6v coil on there, you may have already fried it, or the points. Just warning you.
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My opinion on 6v vs 12v: Leave it as a 6v Truck. after you get all of the kinks worked out, you won't have any problems with the 6v system.
