Changed my water temp sending unit and still nothing on the gauge.

Grounded the outside of the sender "where the wrench goes" to the neg batt terminal. Nothing. Moved the ground to the signal wire and it pegged.

It's looking like a bad sending unit or one that is for an idiot light like mentioned above. I can google it if not, but does anyone know off hand the part number for the factory sending unit? I'm hoping a quick trip to the parts store fixes up my problem. Everything else in the cluster works like a champ.