Jake,
Search in this forum (upper right, under Post Reply and Post New Topic) for "gas gauge" and then "fuel gauge". There are a lot of good advice and diagnostic procedures in old posts.
First you should check the gauge enclosure ground. If the enclosure and gauge are well-grounded, a working gauge should show a non-empty reading (unless your gas tank is empty).
The following things need to be tested (a search will give explanations on how to test) and I would test them in this order:
1. Poorly grounded gauge enclosure. If the gauge is good and the ground is good, the gauge should read correctly or it will spike to full. If it spikes to full, then test for the following.
2. Poorly grounded sender unit in the gas tank.
3. Bad sender lead.
4. Bad sender unit.
5. Poor ground between gauge and enclosure.
6. Bad gauge
Make sure the power lead to the gauge is good.
Of course, if you have a 12 volt system that never used a resistor (Runtz or otherwise), your gauge might be fried.
Tim
