In one hand a multimeter, in the other the electrical diagrams for your engine. First do check the breakers on the engine control box, if any. Our MD22 has two breakers there, older engines had a fuse block instead.
With the fuel gauges failing previously, it sounds like you might have corrosion on the connectors, so worth checking that too. On our MD22 there's a big locking ring plug on the engine and another at the instrument panel. These have brass pins that can corrode if moisture gets in. Cleaning them up (carefully) and applying some waterproof grease/spray sorted it for good.