1995 Ski Nautique Temp Gauge Not Working

Hey guys, putzing with a friend's '95SN that he mentioned that he has no temp gauge. I pulled off the wires off the temp sender on the top of the block, grounded the brown and nothing. Grounded the green wire and it still did nothing to the gauge, but it did flip on the red overheat/oil pressure light in the middle of the dash.

I went behind the dash and grounded one of the studs on the back of the gauge and it spiked the gauge. So the gauge is functional... sound like a broken wire somewhere between the temp sensor and gauge or something else?

Regards,