I had a pre engaged starter jam in on a car, within 20 seconds the motor caught fire as the full amps of the battery ran through it. It glowed bright orange as though it was ready to be thrust under a forge hammer!
A casual look at a few aircraft, the wires seem to either come from the starter solenoid coil or output.
A chappie named Fred kirk, RIP, once told me a tail, he copiloted a Dove or similiar in the 60's or 70's. They had a starter jam and fire. The DofT then mandated starter warning lights.