Originally Posted by Mxfrank

Since neither light nor gauge work, it’s not the sender. Nor is it the cluster. With 99% certainty it’s the ground. The three connections on the sender are ground, float, and reserve light . The float contact will have a variable resistance to ground, this drives the gauge. The reserve contact will connect directly to ground ONLY when the tank is low. My bet, the ground wire is broken or poorly terminated.