Duster temp gauge problems

I bought
Just trying to think of other trouble spots along the way that might cause the issue. Thought maybe the ground in the sensor isn't good enough to get over the hump of resistance somewhere down (up?) stream.

Where did you get the OEM sensor? Was it used?

FYI, I'm struggling with a similar situation.
the oem new on eBay. I think for my next step I’m going to look at the thermostat. Again the car is a new project to me and not sure it’s history. The wiring was a disaster but I’ve made a lot of progress. I can’t imagine that the needle wouldn’t even move if the thermostat was stuck open but I can’t think of what else is going on. I liked the idea mentioned earlier of putting the thermostat in a water at specific temps to see where or if it reads on the gauge. I can keep it attached to the wire and ground the outside and it should read if it’s a correct setup. Let me know if you figure out your issue. Do you have footage at your wire connection?