whats wrong ?

There will be a servo to move the speed wiper across the variable resistor - clearly it's stuck on forward else the motor would not drive - perhaps the servo is broken - perhaps the receiver is asking the servo to move to full travel - perhaps the servo linkage has fallen off. Perhaps the wire between receiver and servo has become disconnected.

I do not know motorised Golf Trolleys - I saw one once - but the basic operation will probably be like a radio controlled model car but with a more powerful drive system.

Good Luck...
August 2015