i have 2 boats as well as my brother ad dad each have a boat. none of the fuel gauges work. can anyone give me a clue on how to get a fuel gauge to work properly? how do they work and where should i start to figure out what is wrong? the sending unit? or the gauge or the wires? all have in hull fuel tanks. the boats range from 1987 to 2001 year models. any help would be great. thanks