[scottyb]

Your problem is in the solenoid activation circuit.

When ever you jumper the solenoid and the cart runs you still have 2 possible problems.
1 would be a bad solenoid & 2 would be a solenoid activation circuit failure.

Or lastly, in this case, a wire in the wrong place! The best thing to do is to get the diagram and sort through this activation circuit wire by wire. You can remove the diode for testing purposes if you are unsure of it's condition or proper orientation.