Motor guide 24V fried??

[Bone1099]

I have a Motor Guide 767v 24volt 67lb thrust manual trolling motor on my boat. I took it off my dad's jon boat working normally. I changed the lead to a round type plug and had planned to run it on both boats. I worked fine on my boat. My dad wired a round type socket into his boat and said it would not work. I connected it to my boat and it would only work in high speed momentary no constant and no momentary although light still comes on and solenoid is clicking. Found a burned spot on the back of the circuit board where the green wire connects and runs down to the lower unit. Seems like i have read that the speed control is in the lower unit with the motor. could it be damaged and if so how can I check it? I do know how to use a multimeter.
Thanks