Trolling Motor and DI Graph Wiring to Batteries

[Kellss]

I purchased a boat last year through consignment at a dealership and was in great condition. Now here is where I am confused (I’m no electrician so I apologize in advance).

I was in the process of replacing the onboard charger with a Minn Kota Precision (MK220PCL) and was reattaching the wiring when I was confused as there were 3 wires coming from the trolling motor (1 red, 1 orange and 1 black). The trolling motor is a 24V motor and has 2 12V batteries powering it as well as 2 graphs (1 on the console and 1 on the bow next to the trolling motor (Humminbird Helix 5 and Helix 5 DI G2). 

 

After looking into it a little more I was able to find out that the 3 wires correlate to a 12V positive connection, 24V positive connection and the negative. It was previously wired as follows (see photo 1):

- 12V positive connection to the positive terminal of battery 1

- 24V positive connection to the positive terminal of battery 2

- Negative connection to the negative terminal of battery 1

- 1 foot cable connecting the positive terminal of battery 1 to the positive terminal of battery 2

- Console mounted graph wiring connecting to respective (positive and negative) terminal of battery 2

- On board charger connections connected up to respective terminals 

 

I read into the manual of the trolling motor and from what I read, it wasn’t wired correctly (which may explain why the previous owner had a battery die and the trolling motor seemed to be slow). The trolling motor didn’t have an option to switch between 12V or 24V like I’ve seen elsewhere, so why would/should both positives be connected? Couldn’t I disregard the 12V connection and wire the 2 12V batteries in series only using the 24V positive connection? 
 

My next concern, I wasn’t able to locate the wiring for the front graph or how it was connected to a battery. I checked and followed the wiring and found it was wired into the Marinco plug (respective positive (using the 12V) and negative terminals) that the trolling motor plugs into (see photo 2 and 3):

Now, with the the graph being wired into the Marinco plug and the positive being on the connection, I wouldn’t be able to disregard the 12V plug (assuming that is the positive it’s wired into). Would I be able to wire the graph back directly to a 12V battery (like the console graph) and then wire the trolling motor in series (disregarding the 12V (orange) positive connection)? If I were to do it like that would it look as follows (see photo 4) (note the disconnected 12V trolling motor connection) and instead of the 12V connection, the bow graph connects directly to battery 1:

- 12V positive connection disconnected and replaced with a direct bow graph connection

- 24V positive connection to the positive terminal of battery 2

- Negative connection to the negative terminal of battery 1

- 1 foot cable connecting the positive terminal of battery 1 to the negative terminal of battery 2

- Console mounted graph wiring connecting to respective (positive and negative)terminal of battery 2

- On board charger connections connected up to respective terminals 

After wiring to match photo 4 and disconnecting the bow graph as to not overload it with voltage the trolling motor is moving much quicker and  more powerful.

If this makes no sense, I apologize I’m really trying to understand this and not ruin anything on my boat. Any help is appreciated.

[MN Fisher]

Don't have to worry about voltage issues...connect everything you want that way...you'll just run the batteries down quicker. I'd balance it by having one graph connected to battery #1 and the other graph connected to battery #2...then you'll get more even draw.

 

One thing...you might get interference on the graphs when the TM is running. I avoid this by having a smaller (35ah) deep cycle to run everything BUT the TM...TM gets it's own, dedicated battery(ies) .

[Kellss]

So how it’s wired in photo 4 is correct? Would I be okay to wire the front graph straight to the battery in the back instead of having it hooked up to the Marinco plug?

[MN Fisher]

It looks right far as I can see - wiring is a little messy. But yes, you can direct wire the graph to the battery...don't forget the fuse - as close to the battery as possible.

[Kellss]

Appreciate the help. I’ll rewire the graph to be direct to the other battery. 
 

and also try to clean up the wiring