Possibly the tan with blue wire that comes out of the boat harness where it plugs into the motor harness?
If I remember correctly it is in parallel with the low oil sensor on the later engines and is not a temp sensor, but rather a temperature switch that sounds the overheat warning horn at the controls.
Sometimes it goes to the area near the plug on the port side and sometimes kind of under the electrical plate where the ignition stuff is connected on the right.
Either way it goes to pin #3 on the plug. When the switch is made it grounds the negative side of the horn as does the low oil switch.
If the oil injection was removed the modifier may have taped up or removed the connection for the overheat switch as well.
