I'm basically re-doing an older Minnkota trolling motor installation.  The motor is a 24v 48 lb thrust bow mount motor.  It's powered by 2 12v deep cycle batteries located in a compartment in the front of the boat.  The motor has a 3 prong pin type plug that fits into a socket near the motor.  The motor only has two wires (black & red) molded into the 3 prong connector.  The manual I have doesn't have any installation instructions for the socket.  When I put the thing in years ago I wired a 6 awg ground wire from the socket to the hull (figured if there was a place for it on the socket it must want one).  Boat is an aluminum hulled fish/ski boat powered by a merc i/o.

So, thinking about it many years down the road I'm not sure wiring a ground wire to the hull is a good idea.  In fact, the more I read about it the more it seems its a bad idea.  The boat will never be in salt water.

Do I want or need a ground wire at all?  The manual is vague, it mentions a fused ground is available if you have interference problems with onboard electronics. That wire is to be attached externally to the skeg of the trolling motor and run to the boats grounding bus or the start motor negative terminal - it has nothing to do with the 3 prong plug.

If I do need to ground it, should I run the ground wire to the main engine compartment and ground to the start battery negative terminal?

I think you need to ground to the Negative terminal of the batteries that run the trolling motor. Ideally a negative buss bar.

Thanks, trying to think through it, doesn't seem like it serves a purpose.  Wondering if I'm missing a safety thing.

Eta: fired an email off to minnkota tech help.  They said no need for a third wire / ground unless we're seeing interference  on boat electronics.

Awesome! One less wire to fool with.

Thanks

Reading more on the third wire.  Early version electric motors often had the capability to run on either 12v or 24v, the third wire is used if thats how your motor is setup. In my case I'm strictly 24v so the orange wire is abandoned.

Thanks KB7DX - you've been a huge assist in getting this boat back on the water!

Ever find your way to Montana I owe you a beer or 4.