Wire it like this. Hook up the 10 gauge wire to the amp meter(terminal that battery isn"t connected to), and the 18 gauge wire to the oil pressure switch,(terminal that battery isn"t connected to). The amp meter should be close to the alternator output amps. They made the delco alternators as low as 37 and 42 amps, but are harder to find. If you are using a 20 amp meter on the tractor keep the engine idled down as much as possible if the meter pegs.