bobshollow,

Your profile says you have a '53 pickup, so that must be the rig in question.

If you do a search in this forum using the word "gas gauge", you will find all kinds of tests to answer some of your questions.

Your rig must have been converted to 12 volts already, as you have installed a new 12 volt gauge assembly. The gauge itself must be grounded in the dash, and the tank must be well grounded too. Properly grounding the tank usually involves a additional wire from a sending unit mounting screw to a good ground on the body or frame. Grounds make this system work properly.

Make sure the power side of the fuel gauge is getting a good 12 volts....no old voltage reducers should be hiding in this line.

I have seen folks here talk about receiving faulty gauges, as these are a real aftermarket specialty item, and QC is sometimes lacking.

Read some of the previous posts on this subject, verify that you have the proper power and the components are properly grounded, and come on back if all these lead to a dead end. Good luck.

Stuart