Thermostat Gauge still not working

[crookedmouth123]

I have had an issue with my Thermostat Gauge not working for quite some time now, I recently did the check with the piece of wire at the fuseboard and the Gauge seems to be working fine behind the dash, So I assumed that it would be a problem with the Thermostat Sender.
I replaced the thermo sender this morning but still no luck, as I was replacing it I noticed there seems to be another sensor there with two pins aswell only one pin is slightly wider than the other, what could this be? I had a bit of difficulty identifying it when I called the part shop, would anyone be able to shed any light on this? could it be that that's causing the Gauge not to work and if not what else could I try?
I am driving a 1.9 TD engine, the engine code is 1Y and i'm guessing it's an old Caddy engine. ( if that is any help at all)

Thanks in advance and wishing you all a Merry Christmas.
Dan.

[MidLifeCrisis]

With the connector going to your new sensor - did you try shorting together the two pins to see if this made the gauge go to 'full hot' - that would confirm that the wiring right to the sensor was good?