Wiring harness

have a Gravely 152 xdz. Wiring harness melted. Replaced it cut the lawn twice, third time caught fire again burnt blade relay wires. Could this be a voltage regulator problem

If you are catching wires on fire you have a negative to positive short. Check for a pinched wire or a relay/switch with a internal short. If its the same wires all the time, that is a very good starting place to look. You should be putting around 14.5 volts to the battery at WOT (wide open throttle).