I have not operated my L 3750 in ages. There is a long black and white wire, 14 gauge on left side of the engine as I sit on it. What does it go to please?
If not, in the absence of a wiring diagram, and seeing the starter is on the left side of the engine, it could be the trigger wire for the starter solenoid.
Is the wire connected to anything? Is it part of a wiring harness or just something added by a prior owner? Will the tractor start and run the way it sits?