We acquired a TW25B from one of our other stores. purchased in the 70's. it keeps shutting off when under any load such as a loading ramp or slight incline. I checked and the batteries were serviced before we got it. I cant find a manual but after talking to the store that had it is has been doing this for a long time. it sounds like the motor is pulling too many amps and the circuit breaker cuts it off. I do not have a manual but I am looking for one. any ideas?