Hi John,
With the battery charged fully. Does everything work properly when it's not locked out? When the power cuts out... Do all three LEDs on the throttle stay illuminated? And stay so with the horn and lights used at the same time? Are the horn and lights operating the same (full voltage) at this time?
I would start by rechecking all the harness connectors and cables for damage, proper contacts/tightness. Looking closely at the battery connector.
Verify that the lower (motor) harness dead ended 4 wire cable is not shorting the wires and terminated properly to prevent this from occurring.
Background information on the battery... Type, size, age, voltage, constant current rating, ETC.
Absolutely intermittent conditions when power lost...? Under high load, near end of charge, bumps?
Do you have the capabilities to communicate with the controller?
Sorry 'bout the 20 questions... getting the facts.
Regards,
T.C.