re: .

You have some decent guesses on what the problem is.
Some people that have guess have absolutely no idea what they are talking about.

If you can find and post or link an electrical schematic I'll give you a good idea of what it is. Everything else is just a guess. I looked for a schematic but I can't find one with text large enough for me to read.

BTW, I still think me and Greasemonkey had the most appropriate response. The radiator cap one was clever though and probably the most correct.