It is aftermarket. Do I measure the resistance across the points on the sender?
What Brand after market gauge is it?
Ive been using a autometer gauge while attempting to get my stock looking gauge to work.
The aftermarket gauge has it own ground.
3 wires comming off the back, Power, sender, its own seperate ground
Have you tested your sender?
here is a video of a test I did on my sender
...video... Its 0-30 ohm