Hi,
Your truck was produced in 1994, it is an old model but I think the controller is smart enough to alarm the error code if it really has problem. In your case, the truck has no drive and no error code this means the truck is missing one of GND singals for the drving enable condition which is not a serious problem. Please check carefully the following posibilities : deadman/foot switch, direction switch, contactor tip, pedal or accelerator switch, check if the brake is blocked,....
Good luck
Nuna