36 electric "trolling" motor
 

I have an electric boat that is pretty cool, I got it for free from an
old guy that wanted it gone from his yard. It has a bank of six 12
volt batteries that power a 36 volt motor that puts out a lot of
thrust. My problem is that the boat got some water in it that
completely corroded the electronic speed control unit. So what I want
to do is directly wire up the motor to the batteries, bypass all the
variable speed control stuff. Problem is, I have three wires that go
into the motor housing, red, black, and a smaller green one. Why and
what is the third wire for? I am not able to get the motor to work
with just hooking up positive and negative wires to it. I believe it
is a Minn Kota 36 volt motor. dan