Trin Indiucator
 

If it is a Merk, there is a position sensor (variable resistor) on the
outside of the drive at the pivot point. I don't recall if it is on the
left or right but one is a trim limit switch the other is a position sensor.

It is common for them to get water inside them and fail. You can verify
this by removing the two small screws that hold it onto the outdrive and
turn the 6 point plastic stud while watching the gauge. It may jump now and
then which confirms that the rest of the circuit is working. If the sensor
is bad, there is not much you can do other than replace it. Sometimes the
wires get damaged but they are stainless steel and difficult to solder. Do
you really need it however? You know where the boat performs best for the
water condition.

Don Dando