1) can you get a dc clamp on voltampohmmeter to measure 12v dc volts at the red hot connection into thruster motor body and compare that at battery + to see if you are suffering significant voltage drop ? and then for good measure check the dc amps flowing through the red hot close to the thruster motor ? (measure volts with engine running, it may be that wire corrosion or a bad ground at thruster end is decreasing the voltage through the hot feed wire.) 2) does your bow thruster require oil additions into its gear leg? if it's not a sealed leg, some thrusters have an auto shutdown so you won't and can't run the thruster motor when it's low on oil. (The Max power 60 thrust I have on my boat has a sealed get leg with no oil top up ever required. some thrusters don't. check with your manufacturer .)