Hi Arrie,
Assuming its not an electrical connection problem. My Yammie trim guage also stopped working a while back, on my old 130HP. Called the local boat shop and there advice was spot on.
The sender is a silly plactic device located on the shaft around which the engine rotates (in the trim sense not steering). This sender pushes on a microswitch which sends the trim position to the guage. Anyway the sender had snapped, a common problem I believe. The replacement is made from metal, you can fit it yourself, provided your fingers are small, and with the help of a small phillips screwdriver.