It’s going to be very easy to test if you remove the sender from the tank.
Connect the + to the sender. Ignition on gauge reads full.
Touch the - to the sender flange and the gage should drop to empty. Because the float is down.
While holding the sender and - wire in contact. Move the float arm and watch the gauge. If it doesn’t move. I’d say it’s the sender. I just installed a new sender yesterday.
Don
