If you take say...a wrench and touch one end to the pos. and one end to the car frame at the same time, all of the batteries power will try to go directly from the frame to the pos. terminal(because the frame is connected to the batteries negative terminal-remember, electricity flows from neg. to pos.)as fast as it can. This sudden, large power flow could create a power surge potential runing throughout the cars entire electrical system. If this potential was great enough to arch accross something, it could easily have melted or broken a wire or other device somewhere in the car. Sounds crazy doesnt it-the adverage static electric discharge of the human body is 25,000 volts. Yes, thousand. Think about that the next time you unload your dryer. It's trouble shooting time for you. Hope you have lots of patients. Good thing you know where the most obvious problem occurs, the instruments(you said guages right?). I agree, get a good wiring diagram that you can read and start looking on that circuit for problems. If you dont have a multi-tester, GET ONE, they are invaluable for most projects and a small one wont run you 25 bucks. E-mail me if you'd like any more tips, I have dealt with this kind of electrical crap TOO MUCH. lol. Good luck.
I had a friend of mine that had a Z without a tiedown for the battery. He went around a corner a little to fast and the battery fell against the engine. The car started running like crap but he drove it until it wouldnt run. He popped open the hood and almost the whole engine wiring harness was fried. It was no fun helping him replace the wiring.