73 Duster after market fuel gauge with stock sending unit

I've posted many threads here on checking out gauges

The QUICK check is to simply unhook the sender wire, ground it, then turn on the key for a few seconds and see if it moves.

Does the temp gauge work?

Here, read this:

http://www.forabodiesonly.com/mopar/showthread.php?t=207604&highlight=gauges