My scooter was a 36V 12A one and I recently upgraded to 48V 20A batteries and a 48V 28A controller. It was working fine but one day, out of the blue, when I switched my lights on at night, the scooter started reversing when I turned the throttle. Switched the lights off and it worked normally. The scooter does not have a reverse switch and apart from that, works just fine. It's pretty cool to have a reverse although I can't use my lights at night. I will probably go see the repair guy since I am in China and repairs are cheap but since I am a hardcore DIY guy, I like to tinker and this problem really baffles me. Any insights will be appreciated and if no solutions forthcoming, I'll post the results of the repair in 2-3 weeks.
Possibly the controller has a wire for reverse that is not connected to anything, and due to a problem with the wiring it is now touching the headlight wire and causing the scooter to go in reverse when the headlight is on.