So you found a burnt solder joint in it? I assume it was on the top deck of the circuit boards inside? That's where I've always found trouble- the one lead comes in from the brake light switch, then splits IN THE SENSOR to feed two pins, one for each light circuit. The single pin is a very high-current path, and eventually is too much for the solder joint to handle.
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Rob Bareiss, New London CT ::: "Roterande Fläkt Och Drivremmar!"

You might check the wiring from the top of the tank. If you can locate the wire from the sending unit perhaps you can ground it and see if the gauge registers full. My GUESS is that the system works on resistance and a full tank raises the float to reduce resistance to register full on the gauge. Grounding the wire as a test might very well isolate your problem area.

Randy

Steve,
You can check the guage/sender unit easily without pulling the instruments out.
Beg borrow or steal a variable resistor (rheostat) with a range spanning roughly 50 to 250ohms,locate the guage wire at the connector in the trunk/loadspace, disconnect it and ground the guage end through the resistor. If your guage then swings through it`s full range as you vary the resistance, the gauge and the wiring is OK.
If nothing happens then the sender unit or wiring is faulty.
Colin.