The solenoid is a safety device. Without it you have no way to turn the power off should anything go wrong with the throttle input device or the speed control.
The speed control will be constantly energized with the jumper on and that is not good for it. It is designed to be on when you push the peddle only.
It is absolutely not recommended to run the cart with the jumper cable on.
The jumper cable is nconclusive testing stunt
