My old trolling motor had three wires going to it. The new trolling motor only has two both are 24 volt systems

SOURCE: Converting From 12/24 to Starght 24 Volt

if it is 24v. then you need to connect 2 battery in parallel. since the battery is only 12v.
if one battery is shoing red and the other is sohwing green, that means you are using 12v only, not the 24v.
connetion as follow:
positve of battery 1 to the motor, the negative of battery 1 to postive of battery 2. the negative of battery 2 to the motor.

SOURCE: Need to know how to wire a motorguide 767 brute trolling motor

The white wire is the ground. The black wire is neg. and the red wire is pos.

SOURCE: wiring diagram for 12/24 volt system

here is a wire diagram. follow the pictures. you can do fuses but i like inline breakers. you can get them at your local outboard dealer.

SOURCE: i bought a used trolling motor (motorguide brute

the black wire goes to - and the red goes to + for 12 volts. If you want 24 volts you need to add another battery and run a jumper wire from the - of the first battery to the + of the second battery and hook the white wire to the - of the second battery. Here is a picture to help you.

SOURCE: Wire going to prop of Motorguide trolling motor shorted

Unless you are mechanically inclined, dont attempt this. Take the lower unit apart by removing the prop and removing the two bolts that hold the forward and aft housing to the center housing. Fwd being the cone shaped part. Pull the aft housing away from the motor so you can inspect the connections to the board that holds the brushes and the soldered wiring terminals. You should find the solder missing from at least one of the terminals that connects the wiring from the foot switch to the speed control windings inside the aft housing. Clean up the terminal and wiring and re-solder. Also re-flow the solder on the other terminals. Clean up the seals and the area where the seals meet the housing parts. Replace seals if damaged. Reassemble the lower unit and torque the bolts 45-50 in-lbs and no more otherwise you will fail the seals. This problem is due to a "cold" solder joint that creates a high resistance to elec current flow and heats enough to melt the solder. This is a result of poor quality control at the manufacturer. Good luck.