Switching over from an ancient 45# motorguide to a 74# Maxxum hand control. The motorguide was 12/24v so I have the batteries in series with 2 positive wires and one negative wire going to the bow. I understand that because I could select between 12 or 24 volts on the TM. The Maxxum is a 24 volt. There isn't a switch to go from 12 to 24v. It has 4 wires running from the motor. 2 red and 2 black. All of the Maxxum user manuals that I can find online, show that I should be running one 24v wire to the TM. Why would the TM have 2 positive wires to connect if it is only 24v? This model has the digital maximizer, could that be the reason?

I was going to just hook the 2 reds up to my current 2 reds and the 2 negatives to my one negative but now I am second guessing if I will really have 24v going to the TM properly. I am confused on the proper way to continue.

Negative, wrong move. The two red wires in your boat are currently at different voltage levels (12V and 24V) - if still the way they had been connected previously. Connecting those two reds together will short a battery, and without a breaker it will melt wire and possibly blow up a battery!

You said you have the batteries connected in series. That's good, and I assume there is a short wire between one battery positive and the other battery negative to do this.

Remove the red wire originally on the positive terminal with the battery-to-battery jumper. Reconnect it to the same terminal with the other red wire (which is 24V). Now you have TWO leads for 24V, which will carry more current than a single wire of the same size. Treat these two red wires together as your "24V lead". You have the wire, so use it - you'll get more power, trust me.

You did not say what gauge wire you currently have. For a 74# motor it should be 8 gauge wire at a minimum, and 6 gauge is preferred for better performance (less voltage drop). I hope it's 6 gauge. It should be marked if you look on the insulation jacket. If #6 wire, use a 60 amp breaker. Please don't skip having a breaker. You didn't mention one; the available current can burn a boat without a breaker. Ask if you need recommendations.

As for the 2 red and 2 black leads. You said "on the motor" but I guess you really mean the power cord itself and not what goes down the shaft to the motor. They might build multiple models using the same power cord, whether 4 leads are needed or not. Or, a service tech could have used what was available even though the unit only needed two wires. Open the head to find out if all 4 leads go down the shaft to the motor. I bet they do not, so two of them will do nothing in that case.

Bobby,
Flippin-out's advice is well meant, but can likely get you in trouble.

First, every Minnkota I've seen has two wires, red/hot, black, ground. If yours has 4, call MK's cust service with your model and serial number and have them verify which wires to use. Anything else is going to be a guess.

Secondly, The existing wiring in your boat is likely, bare copper, and SAE grade. SAE is smaller wire per gauge than AWG and will conduct less current and drop more voltage. Also, you do not want to combine wires to increase current capacity, as that does not always give the desired results.
Do it once, do it right. Use NEW #6 tinned marine cable to run a hot and ground to the TM. Use the appropriate size lugs and crimp them with the proper crimping tool, then seal them with adhesive lined heat shrink tubing. Use tinned copper lugs as the plain copper ones are too soft and do not crimp well. If you don't have a crimp tool, have someone do it for you. West marine sells a lug crimper that you hit with a hammer and it's junk.
For the cable that connects the two batteries in series, use #6 cable as it will carry the same current as the long wires. They are connected neg to positive and the outside battery post are the ones connected to the cables going to the TM.
The wiring from the TM head is probably #8 wiring which is OK for that because it is a short run, but that size cable is too small for the long run from the battery.
You'll need a way to connect the battery cables to the TM wires as they are gong to be different sizes. If you get advice on here to simply solder them, ignore it. Anyone who says to do that has probably never done it. Plus, soldering is not acceptable by ABYC as the sole means of making a mechanical connection. You can not get the cables hot enough to flow solder with less than a torch and you'll burn up the insulation on the wiring. Blue Sea makes something called a power post. You can see it on their website. Use the appropriate crimp on terminals for the different size wires and connect them at the power post. This makes a secure, reliable connection and also makes future removal of the TM easy in the event you need to do that.
The wire from the batteries has to be protected. You can get ANL fuses that will work, but a surface mount circuit breaker is the better choice. Blue Sea also makes those. It needs to be mounted as close to the batteries as possible. it's purpose is to protect the wiring in the event of a short, not the TM.
BTW, I am not on retainer for Blue Sea, but I have used their products for over 20 years but I believe in them. They work, and they are reliable.
Cheap does not work well with quality or reliable. In the over 20 years I have been doing this, I have seen very few problems that were not caused by either cheap materials or shoddy installation.
Feel free to PM me if you have questions and I'll be happy to help.

Ok mystery solved. My wiring is new #6 marine cable. It does have circuit breakers, one for the 12v and one for the 24v line. Part of the serial number was too faded to read. I called MK this morning and talked to them. They advised that their newer TMs have 2 wires. Some of the older units have 4. If it has 4 then I put the 2 reds together and the 2 blacks together and wired it as a 2 wire 24v system. I also have a new MK circuit breaker and am going to replace the old breaker with this.

Thanks for all the help guys.

Bob, I call BS on saying any of my advice will get the OP in trouble.

While I do not care for #8 wire, Minn Kota's own technical guidance says it is acceptable for that motor. Some people don't have a lot of $, so if they have #8 and MK says it is ok, then tell me where that is wrong. I have MK's link if you need to see it.

I said he needed at least #8 wire, then I added he can double up for more performance because he already has 2 runs of red wire - with the requirement that each be at least the stated #8 size. The double-up is not mandatory - either run is sufficient per MK. Two #8 wires will provide more equivalent copper cross-section than a single #6 and can actually carry more current. If the breakers are kept on both runs, there is no danger in this, and less voltage drop results. Please point out how this "may not provide desired results".

I did not get into whether marine wire was installed. I see quite a few boats that come from the factory with it, so until I see it isn't marine wire, I'm not going to bring that up. The other details were already long.

Most people aren't equipped to crimp heavy wire like you or I are. I didn't bring up termination either, so I didn't steer him wrong on what I did not discuss. The hope was he would be able to simply reconnect what he already had without doing any advanced termination.

Thanks to everyone for their input. I have it installed and it runs! Waiting for the storm to pass to try it out.