I don't know your model, but the circuit breaker is easy to trip when running flat out for extended periods on some motors. I don't know where the circuit board is, I suppose inside the housing. But when things like these motors fail there's usually a part on the circuit board the shows heat or a component shows heat damage. If you do have a damaged board, and the manufacturer is no help or too expensive, there are people online that fix circuit boards of all kinds. Sometimes the heat unsolders components. On electric outboards I have owned, most have wiring that barely meets the amps at full throttle and if you extend the wiring you'll have trouble. The longer the wire run, the bigger the voltage drop. As the battery gets discharged, running at full throttle will cause the motor to draw more amps as the voltage drops. So a battery half discharged will cause the motor to draw more amps, possibly more than your circuit breaker.