Rich is correct. In my case, however, I was able to replace the wires from the gauge sending unit to a point before they entered the transom. The insulation had simply cracked and water had corroded the wires.
Similarly, many years later I was having problems with the trim itself, intermittant action. I examined the throttle switch several times, replaced the pump solinoids and more until I recalled the gauge problem I had earlier.
Sure enough, insulation had cracked and the trim sending unit wires were shorting out against the bell housing. Another external fix and I have been on the water since.
When I eventually replace the bellows and the shift cable I will properly replace the 2 sending unit wires as well.
1990 23CSS - one of the last ones built
South Central WI