The trolling motor on my recently-bought boat has an upper unit marked "Motorguide Brute Mod. 750 12/24 volt 45 lb. thrust", but the lower unit, which is the electric motor, is labelled "Whisperguide Propulsion System 41 lbs Thrust". Obviously, someone has changed the lower unit. My question: Is the existing lower unit (the 41 lb motor) also rated for 24 volts? I am currently using it on 12 volts, but want to wire it for 12/24. Thanks.