[Lochlin]

You have the wiring diagram, correct?

Completely forget the wire color as that can change over the years.

I think your best tact is to use your 4 post solenoid only. It's what the cart was intended to have and it will remove any unknowns.

Take all of the wires off the solenoid. Now, simply redo everything exactly as it is on the diagram. When you are looking down at your solenoid, and all of the terminals are pointed away from you:

1) The left terminal (large wire) goes to F2 on the starter.
2) The next terminal (small wire) goes to the microswitch
3) The next terminal (small wire) goes to ground.
4) The next terminal (large wire AND small wire) the large wire goes to battery + and the small to the circuit breaker.

I think whoever put that 3 terminal solenoid in there had to fiddle with the wiring to get it to work. If it were me, I would probably start from scratch and rewire the entire cart from point to point to make sure that everything is going where it is supposed to.