Before replacing the sending unit/floater assembly I would make sure that it's not something else (relay, wire, or a faulty gauge).
If the gas gauge doesn't move (stays on empty) when the ignition key is turned to the "on" position, current may not be reaching the gauge. Connect a jumper wire between the ignition switch and the dash gauge. If the gauge now works, replace the defective wiring between the gauge and the ignition switch.
If the gauge reads high at all time, try grounding the tank unit electrical terminal to a good known ground (clean chassis). If the gauge jumps to empty or below, the tank unit is OK, but there is a bad ground between the gas tank and the body or chassis.
As far as the interior light, do you read a voltage at the bulb? You could have a faulty wire, faulty ground connection etc. My guess is that if the light doesn't even come on, not even dim, there is no current reaching the bulb meaning that you have a problem in your wiring like an open, bad ground, superduper high resistance (less likely if your bulb is completely out and not at least a little dim), or your bulb is broken (that would be the easiest fix).
Monday, November 19th, 2018 AT 5:39 PM