Toyota Repair: Rear demist switch & fuel gauge, toyota corolla seca, fuel gauge

Question
I have a 1986 Toyota Corolla Seca in Australia, with 380,000 kms on the odometer. Car is excellent, reliable, economical, in fact, my friends have complimented me on owning a 1986 car which looks so new (I bought it secondhand, and have owned it since 1993). Apart from general wear and tear items such as tires, brakes requiring changing, the car has proven to be incredibly reliable. There are a few niggling items which isn't working though. One is the fuel gauge, and the other is the rear demist switch. Neither are working. Any tips as to how I can troubleshoot them? I've checked the fuse for the rear demister, but that is fine.

Answer
The reason for the rear defroster grid not working is normally because there is a break in the grid lines somewhere or one of the electrical connectors on the glass has broken off, you need to remove the rear side trim pieces to get to them, while you are there check for voltage at the terminals one side should receive 12 volts to ground, use a test lamp, if there is a break in the grid it can be repaired by soldering the break back together, the trick is finding where the break is, you can co this by groundin one side of the testlamp and the puncturing the grid at different places, you will find the break where the light no longer lights up, sounds a little complicated but at least you know the theory.
The fuel gauge not working is normally the fault of the sending unit in the fuel tank.