On many mowers that have a 4 prong flat connector, there is a shorting tab in the mowers end connector. You'll see little tabs if you look at it from the open side of the connector. If you put an ohmmeter from pi to pin, they'll all measure 0. It's been a while and I don't remember wither you will yank the shorting tab out from the open end or wire end. Try open end first. I got it out without damaging it, so it can be replaced after troubleshooting. Leave the switch unplugged while testing. Worse case, you could cut the connector off and reattach it later.