How many wires on the back? The simple ones on boats are just two wires, a power and a ground.
If that is all it is, you can remove it and hook up wires direct to a battery. If it spins, its good. If not, time for a new meter.
If that is all it is, you can remove it and hook up wires direct to a battery. If it spins, its good. If not, time for a new meter.