[GMCDAC]

You're welcome, Hantke! I currently don't own one of these trucks so I don't want to get too detailed about the electrics and normally when I get done writing what I know my explainations become clear as used motor oil!

My '55 GMC grounds through the frame and sheet metal, so on a lot of the stuff, there is no ground wire. It is the negative side of your battery. Without a ground or a dirty ground electrical components will not work or in the case of lights, resistance in the ground will make a dim and erratic light. The dimmer switch does sound like it is dirty or corroded since you were able to get them back after the double-tap. I think they are pretty cheap. I haven't had to buy one for quite awhile.

A bus bar sounds like a "jumper" to eliminate the fuses and I sure wouldn't recommend it and yes if you used it all electrical components would require individual fusing. Your test light won't do a great job finding bad grounds but it can be done. An ohm meter can tell faster if grounds are bad.

Do you have a Harbor Freight Tools store in your area? Sometimes they have Volt-Ohm-Amp meters like this one free with a coupon but normal price I think is around 10 bucks. I rely on HF a lot.

That shop manual would be a good idea probably but I really can't say there.

DAC