question on tilt / trim Gauge...

I just Acquired a 1987 Four Winns Horizon 170... All Gauges work except trim / tilt ... The only one I do not know how to fix... I have only had outboards before this and 2 of them had electric trim / tilt and no gauge... never had any issues... Now I am finding myself not being able to maneuver in sallow waters ( 3 - 4 ft) without dragging outdrive on bottom... I would like to fix gauge but in the mean time is there some way to judge where outdrive is ? I have tried timing works ok but I have to stop & start over each time I through a Tuber off... and also any help with the gauge would be grateful....
Thank You
Ken D.

Now that I have forgotten to give additional info --- this is an I/O with merc. outdrive -- tilt / trim is a single button operation and works fine... it is just the gauge.. any info would help