If he went from battery + to the side of the sending unit, yes, the light should come on. It's going to ground, just like grounding it anywhere on the engine. But is it a GOOD ground? Get that teflon tape off the sending unit and out of the threads on the manifold. Then use an ohmmeter from the sending unit housing to the manifold. It should be at or near 0. Then you know you have a good ground. Then test the operation of the sender as Mike69cuda outlined. With the ohmmeter + lead on the sender lug and the - lead to ground, you should have (I'm taking Mike's word on this :) ) 60-80 ohms. Warm up the engine, and take the measurement again. You should have 20-30 ohms. If either reading is off, you have a bad sender. Period. As long as you confirmed a proper ground, and you have confirmed voltage and gauge response as previously posted, that's all it can be.
