D4 260C Trim stuck at 56

Have a trim gauge always reads 56 degrees up, alarm is on, jump trim pump to raise or lower outdrive gauge doesn't change. Tried switching with a known good sender and slowly turning knob, no change. Have up to 9.5 volts input and should be around 4 or less, only sensor on vessel that has high voltage. Tried swapping the harness from sensor to first plug at trim pump, same thing. Was advised to try the dc converter with another known good one, no change. Pin test shows high ohm reading on that circuit but it fluctuates. Anybody seen something like this before? any advice would be helpful, salmon season opens soon.

A high ohm reading would explain the higher voltage,but a ohm reading that fluctuates would point to a wiring issue,a bad ground?

Thanks for the reply, beginning to think it has a short to power somewhere in main engine harness. Pulled every ground and cleaned shiny, even ran an extra6 gauge temp ground from battery to block, no change in voltage and ohms still changes. Also noticed the EVC gauge will come on briefly when turn batteries back on at new vsr assembly, didn't see this till a friend came over and flipped the switch while I was in the cabin, can't be in two places at once.