A simple Potentiometer can duplicate the Ohm's needed for the module to trigger the ground. Typically 10 or less. Twist up and down to makes sure it goes on and off.
Or without the trip to RadioShack just trick the gauge into seeing zero Ohms. Do this by disconnecting the lead in the trunk from the fuel tank sender unit, then ground the connector that runs forward to the gauge. Your gauge will peg empty when you power up, and if the module is working it will trigger the ground and light the FUEL light.
If not chances are the module is dead and you can replace with factory style, or a variable that you set the trigger point so it can be a bit higher then the typical 1/8 tank.
Attached is the design of the original modules from a thread I started a few years back over at Team Camaro. Lots of tips and tricks in that thread to customize your trigger point.