Hello fellow fixer. My first post here, no applause please. I'm thinking the start button operates a relay, which in turn carries the high current for the starting motor. Much as it is done on automobile gasoline engines. If that's the case, I would suggest inspecting the wiring both from the starter switch to the relay, and the relay itself to the starter motor. Both the relay and the switch require a connection to Battery + as well You might find damaged wiring, cracked insulation, corroded connection points. In general with DC circuits, undamaged wiring and clean tight connections are essential. On the other hand, in your case perhaps the switch itself is supposed to carry ALL the starter current. Then it's a good bet the switch (which has electrical contacts, like any switch) got (carboned up (technical term) or even pitted by the arc jumping just as the contacts connect. Any crud on electrical connections can corrode and create unwanted electrical resistance, and may become very warm as the corrosion...