Is the light flashing a repeating pattern, the trouble shooting suggests a continuous flashing indicates low battery voltage at the controller. Check the voltage at the controller. first with the handle up, then pull the handle down.
Battery voltage is low.

Controller voltage calibration is incorrect.
Compare the at Battery voltage to voltage
measured by an accurate digital voltmeter between
B+ and B terminal. Pull down tiller handle
to engage contactor for this measurement. If
these two voltages are more than 1 volt difference,
do the following:
Check for shorts to frame
Check at the connector
Check at the contactor
check if contactor engaged.
Defective or damaged connection to battery.
Inspect cable crimps and cables from battery to
connector.
Inspect cable crimps and cables from battery contactor
to controller and contactor.
Verify the voltage on the controller when the main
contactor closes.
If voltage is less than 21V, check the battery,
power connector, fuse, main contactor.
If is higher than 22V, most likely is the controller
Try draining the controller and repowering it
The ZAPI controllers can hold an electrical
charge for several minutes after the key
switch has been turned OFF. To prevent injury,
discharge the controllers by connecting
a 200-ohm, 2-watt resistor between the battery
positive connector and battery negative connector
on the controller and hold there for at least 5
seconds.