Still have that receipt?

Hi Kevin,

Just purchased the 2501 battery isolator for my boat. Going to use a two battery system, one for starting, and the other for trolling motor and accessories. I have an outboard mercury 70 hp motor.

Do I need to come directly from the alternator to the isolator on terminal A? If so, how is that done? And do I use the existing alternator wire, or add a wire from the alternator?




You need to connect the isolator directly to the alternator output. The alternator sense wire needs to be connected to the positive post of one of the batteries. This can be difficult with an outboard motor and impossible on some models.

I would strongly recommend returning the 2501 battery isolator and purchasing a VSR based automatic smart boat battery switch. This unit will allow you to charge two batteries with your motor, but does not require you to connect to your alternator output. The VSR connects between the positive battery posts and monitors the voltage on each battery. Your outboard motor connects to one battery and your boat accessories connect to the other. The grounds are tied together.

Hope this helps,


Plug Polarity Problem?


I bought the Marinco Connect-Pro trolling motor plug and socket set about a year ago and am just getting around to installing it.

Unfortunately I don’t have the paper instructions any more.

I see the terminals are marked 1, 2 and 3. I have a very small 12 volt trolling motor, and will only use two wires, red and black. Marinco Connect-Pro Trolling Motor Plug

Looking at the design of the plug, I think I’ll be using terminal 1 and terminal 3 and leave number 2 unused. My question is whether the red positive lead should use terminal 1 or 3.

Thanks for your consideration.



It doesn’t matter which terminal you use for + and which one for -, as long as you use the same wiring arrangement on both the plug and receptacle. My preference on the Connect-Pro system is to use terminal 1 as ground, terminal 2 as +12 volts, and terminal 3 as +24 volts.

Happy boating,


Reconnect Batteries in Series?


I have a foot controlled trolling motor with a toggle switch to go from 12 to 24 volts. I have a plug at the trolling motor that runs back to two 12 volt batteries that are not wired in series and I also have a three-bank battery charger for starting battery and both trolling batteries.

The trolling motor will only work when toggle switch is set to 12 volt. Do I need to wire the trolling batteries in series?Attwood battery boxes are safe and economical




How many wires are in the trolling motor plug and wiring?

  • If there are 4, the system is designed to use the 12/24 volt switch to switch the trolling motor from parallel 12 volt to series 24 volt. Something is wrong with the switch or wiring that is preventing this parallel to series conversion.
  • If there are 2 wires, the 12/24 volt switch will not work. The system will either be 12 volts or 24 volts and cannot be controlled by the switch. Connect the batteries in series to run your motor on 24 volts.
  • If there are 3 wires, the 12/24 volt switch is designed to switch between 12 volt single battery and 24 volt series battery. This system requires a jumper between your two trolling motor batteries.

Hope this helps,


Using 12 Volts of a 24 Volt System


I bought a 24v trolling motor.

When I wire the motor using a 24 volt connection, does that preclude me from using those same two batteries to power other 12 volt applications, such as a power anchor? MotorGuide builds the world's finest trolling motors




You can certainly still use the same two batteries to power other 12 volt applications.

Be extremely careful when connecting items to the battery that represents the 12 to 24 volt portion of your trolling motor system. I would recommend circuit protection for the negative leads of 12 volt devices connected to this battery.

For example:

You have an aluminum boat. You connect your power anchor to the 12 to 24 volt portion of the trolling system. Your main engine is connected to the the 0 to 12 volt portion. The engine bolts to the transom. Now the entire boat is grounded.

Suppose that something happens to your power anchor and its power and ground wires short to the hull. The fuse on the positive lead for the power anchor blows. The negative lead doesn’t have circuit protection and it causes a dead short through the hull, through your main engine, and back to the negative of your 0 to 12 volt battery.

Let me know if you have more questions,



Thank you for the prompt rely.

I have a separate battery for the motor, so hopefully this will simplify things. Are there any concerns I should have with battery chargers wired to each battery?




Make sure your battery charger is designed to charge a 24 volt marine electrical system.

A dual-output charger with only a single ground will not work. Each charger output needs to have a separate, dedicated ground.