Electrolysis is corrosion caused by the flow of DC electric current through water. Compared to other forms of corrosion, electrolysis is quicker; signs of corrosion will usually show up within a couple hours of use. Typical signs of electrolysis are a white powder on aluminum parts, especially at seams or sharp corners, or the actual loss of metal.

Battery Selector Switch

Battery selector switches like the one shown in the image below allow the user to disconnect their starting battery during charging, connect their starting battery when they want to use their boat, jump start their starting battery by paralleling another battery to it, or run their boat off of that second battery. In most selector switch installations, the second battery will be one of the trolling motor batteries. If wired correctly this is a perfectly acceptable accessory. If wired incorrectly this can be the source of serious electrical issues.

How the Switch Works

The switch has outputs that your outboard and 12 volt accessories should be connected to and 2 sets of inputs (one for each of the two batteries that are to be used). Internally the negatives or black wires are always connected to each other; the switch only switches the positive or red wires. When in the OFF/CHARGE position no red wire connections are made. In the ON/RUN position the positive wire from the input is connected to the output. In the JUMP START position the positives from both batteries are connected to the output (and each other). In the BATT 2 ONLY position the positive from the second battery is connected to the output.

Correct Wiring

If the low side trolling motor battery is used as battery 2 for the selector switch this will not cause any issues. The diagram below shows a switch wired correctly. There is no voltage potential between the trolling motor case and the outboard case.

Incorrect Wiring

If the middle or high side trolling motor batteries are used as the second battery this will cause issues. Using one of these two batteries creates a voltage potential between the trolling motor lower unit and the outboard case of either 12 or 24 volts, depending on which of the batteries is used. With this voltage potential present electrons will move from the trolling motor lower unit to the outboard lower unit or other grounded items below the water line; these electrons carry aluminum molecules with them causing rapid corrosion of the trolling motor lower unit, this corrosion is called electrolysis. The images below diagram the incorrect wiring of the switch.


  1. Ensure that this issue is not due to saltwater corrosion on a non-Riptide motor. Saltwater corrosion on a non-Riptide model is not covered by the Minn Kota warranty.
  2. If the motor is a 24-volt or 36-volt model, is the crank battery being used as one of the trolling motor batteries?
    • If no, go to Step 3.
    • If yes, ensure the crank battery is the first battery in the trolling motor battery system. (The negative lead of the trolling motor should be connected to the crank battery.)
  3. On Maxxum/Fortrex models: If the motor is a later model Universal Sonar (or any US motor that has had an internal ground / bonding wire installed from the brush plate mounting screw to the directional indicator light circuit) ensure the ground is connected to the negative (-) side of the indicator light.
    • If you are not sure which wire is the negative (-) side, power up the motor and turn it on (the light is designed to have voltage applied to it when the propeller is spinning). With your VOM (multi-meter) set to check for VDC, touch the probes to either wire on both sides of the indictor light. If you have a +12VDC reading, the negative side is the one that your black probe is touching.
  4. If the steps above do not resolve the electrolysis issue, we recommend taking the motor to an Authorized Service Center.
Was this article helpful?
10 out of 17 found this helpful

Articles in this section

See more