1978 c-81 with a 1993 12hp kohler

[canam1991 2]

I just put a newer coil less 12hp kohler on a 1978 c-81 i used the older wiring harness on it i can get it to start and runs but when i turn the key to off the motor keeps running. there is a black wire on te switch that i can not find a home for the motor has two wires coming off of it a purple and a white. where does this black wire go to kill the engine?