I have a 1990 FLHS that has a non-functioning fuel gauge. I am not sure if it's the sending unit or the fuel gauge... is there any test to perform that will give you where the problem resides? I took the float out and it moves, but when the bike is turned on, there still is no registration on the fuel gauge when the float is moved up and down. Any ideas?

 

Measure the resistance of the sender. Move the lever through its arc and observe the resistance changing. If it's open or jumps around, the sender is bad.

 

Somewhere in your service manual it will say the resistance in ohms of your sender should be around 40 at one end and 250 at the other. Moving the float between those extremes it should vary between those. Essentially the gauge is an ohmeter, so there may be a test in the manual for that. Otherwise follow the wiring through the bike to check all connections are sound.