Need trolling motor 24v / 3 bank charger wiring hookup help

Each battery gets its own bank even though they are in series.

I’m not quite sure what you mean but you will have:

Battery one
positive (+ to tm, + from charger)
negative (- to + on battery 2, - from charger)

Battery two
Positive (+ to - on battery 1, + from charger)
Negative (- to tm, - from charger)

Negative to negative maybe suggests the previous owner was running those batteries in parallel.
What do you mean when you say circuit board? Are you trying to run something other than the trolling motor off of this?
I would find out what the red wire is coming from, you shouldn’t be welding the terminal to the post by just connect the negative from one to the positive of the other with nothing else connected.

the second red wire was another positive to the trolling motor.

and he had that small jumper cable from one negative to the other negative. however there was NEVER another second negative wire coming from the trolling motor, only that single one. So two hots and one negative from the trolling motor.

i took off the #2 red altogether and put the bigger jumper cable on and it got a lot of power, the full 24V I'd imagine.

so did he have it right the first time and the jumper was just too small?

thanks for your time.

maybe so. thanks for the help.

You can jump your starting battery off of one of the trolling motor batteries but it has to be a certain one.

I think the one that the trolling motor negative goes to will cause a short.

Best to just disconnect the jumper wire between the two.