[franken]

I'm recalling something more like TU65 sender, but don't trust my memory. I recently read that new sensors are inaccurate.

I'd measure the voltage to ground on the sensor and across the gauge to get an idea of what's happening.

I think most meter movements (the bit that moves the needle) operate on voltage. Based on that, I'd guess the sender is a heat controlled varistor of some sort.

You want to figure out what range of voltage the guage wants and the range of resistance the sender has, then decide how to approach the problem.