You may find it helpful to identify the issue number of the controller. Faults Index Controller is dead Controller will only go in one direction. As you advance the controller from zero speed, one relay should click in forward direction and the other relay should click when reverse is selected. Same relay clicks, both directions . One relay clicks, other does not .
Relays click properly .
Read Pro, Scoota and NCC series controllers internal power supply and protection circuitry . If any accident occurs to the board, it is designed to fail safe and in particular, the zener diode may fail short circuit. There will then be zero voltage across the pot. If it is correct, the current source is working. See NCC series controllers, key components to identify the zener.