Starter keeps running
The relay welded itself shut. Replace it and you should be good to go.
Not necessarily, but might be.
Geezus some of you guys love to spend other guys money
"It could be" the relay
Do some checking, first.
Look at the relay. Notice the small "push on" connectors. These are the relay coil (magnet) connections. One goes down to the neutral safety switch, or if stick, in to the clutch switch. The other comes from the ignition switch.
Next time it does this, pull off either one of those connectors. If it quits, it's either NOT the relay, or pulling it off jiggled the relay and broke it loose.
This could be a bad ignition switch, and in some rare cases, problems in the starter wiring or solenoid.
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It the above did not work, unbolt the wire going to the large exposed "square" terminal on the relay. Hook up the battery. No crank? Jumper the wire you just disconnected to the large battery stud. It should crank. should stop when you let off. It does? Replace the relay
It keeps going with that wire disconnected? Problem is in wiring down to starter "welded" to battery or problems in solenoid.