I currently have a 56 # 12/24 Motorguide Brute on my 98 Xpress. Just picked up a 70# X3 Motorguide for an upgrade. Will the wiring on the plug and batteries have to be changed since it is wired for 12/24? 40 amp breaker good for this new motor? I'm thinking the wiring has to be changed but wanted others opinion on this.

My new to me Triton had a similar setup - 12/24 MG. This was replaced with a 24V MK. There were two sets of black/red wires running from the TM batteries to the front. One set of black/red was disengaged and just sits in the boat. I can't pull it out because it must be zipped tied along the gunnel from back to front where I can't get to it. So the extra wires just remain where they are. Yes, I had to change the TM battery connections for full 24V. There are many schematics on the forum showing this configuration as well on the Internet. I also had to change the outlet plug at the bow on this boat. This may or may not be true for you. I did this myself and I am no electrical whiz.

Read the manual. The proper amp breaker to be used will be described and do replace the existing breaker if it is not the correct size.