Sometimes a faulty ground connection can cause similar symptoms, but as yours also has a problem with the main cable disconnected, it is unlikely to be a ground connection problem.
It's more likely that you may have some water that has found its way into one of the connectors, or perhaps into the controller itself. Has it been ridden in wet weather recently, or perhaps washed off with a hosepipe etc.?
Check the big multi-junction block on the motor harness and see if there are any gaps where the wires enter the unit.
Sometimes the surface water on the road gets thrown from the tyre straight onto the connector, and capillary action will soon help the water to get inside especially with a very tiny gap.
If you can't find anything wrong with the motor wiring or connectors, I would suggest removing the controller to check for signs of water inside the controller housing.
AlanP.S. If you bridged the throttle connections
before the power was turned on it will not operate the motor due to a safety feature which prevents the bike from taking off if you accidentally turned on the power with the throttle activated.
