Audiofn

You can short down the Send side of the guage and it should jump up to full. As has been said there are going to be 4 wires that come into the engine bay from the drive. One pair of those is a wire for your trim the other pair for your trailer trim. On the pair for the trim One side goes to ground the other to the guage..... Make sure that the one side is going to ground. This is one of those things that if you are there it can be diagnosed in a min if not...... we are hear for ya buddy Do you have a multi meter?

ThirdBird

The problem is most likely the rotory sender itself. They leak after time and corrode all to hell. I'll bet you a six-pack; open the sender cover and you'll find nothing but a corroded mess. New ones are easy to install except for the wiring. They come with wiring and seals intended to penetrate the transom assembly. It's easier to cut/splice/heat shrink the new ones.

pshannon

Exactly...they swing up..