Well you need a known resistance to apply to the gauge instead of the sender. Since "we" don't have radio shack anymore, you likely have no local supplier to get some test resistors.
One way to "quick and dirty" is some small 12V lamps. rummage around do you have any cluster lighting bulbs, etc. As a random example, you can Good "no. 57 lamp specifications" I just picked that lamp out of the air. google says it is 14V, .24A If you plug that into ohms law (R = E/I or Resistance = volts dlvided by Amps) it comes out 58 ohms. THIS WILL NOT BE terribly accurate because resistance changes as the bulb heats and cools. But 2x no 57 lamps in parallel should give you "somewhere" in the 1/2 scale reading range. Even one bulb---you can put on the temp gauge and see where it reads, then hook to the fuel gauge sender wire and see if the fuel reads the same.
