Probably Polarity


I need your assistance with my boat wiring.

I have changed trolling motor batteries in my boat and since, I have burned 2 twist plugs. My cables aren’t marked so is it possible I may have crossed them or is that something that would cause my dilemma.

What could be causing me to burn the plug? It has a 4 wire Marinco outlet.

Thank you


On a 12/24 marine electrical system, wiring the batteries is critical. Use a meter (not a test light) to determine if the polarity is correct and the battery cables are correctly connected.

The circuit protection in the positive leads at the battery should trip before you burn up the plug. If you don’t have fuses or breakers at the battery, now is a great time to add them.


New BEP Digital VSR

One of the world’s top suppliers of marine electrical products, BEP Marine, is introducing a new digital voltage sensitive relay. It replaces the company’s well known VSR, which is hugely popular and is considered essential on any boat with more than one battery bank.

The DVSR, which functions as an automatic smart battery switch…

…allows charging of two independent battery banks from a single charging source. When the voltage on the start battery rises to a charged level, the DVSR engages allowing the 2nd battery to charge. When charging stops and voltage falls, the DVSR will disengage, isolating the two batteries from each other. Dual sensing functionality enables the sensing of two battery banks, allowing two way charging.

Here is an earlier post from our site explaining the VSR in detail.

According to BEP, their new DVSR offers a number of advantages over the older version. They include:

  • 80% lower stand-by current draw during normal operation when powered but disengaged
  • Zero stand-by current draw when remote sensing circuit utilized
  • Multi voltage – auto selects between 12V and 24V DC operation
  • Remote status LED output. Provides DVSR status indication at remote location
  • Remote sensing circuitry provides isolated control from secondary supply, and enhanced protection from voltage spikes when connected to ignition switch
  • Increased accuracy of voltage measurement through digital circuitry
  • Lowered cut in voltage from 13.7V to 13.4V (26.8V for 24V) to suit low output alternators, and high temperature environments

Boaters who want to upgrade to the new BEP DVSR will find it on our sister boat wiring site, EzAcDc later this summer.

Mystery Part Identified

Dear Kevin,

I just bought a used pontoon boat and it has a battery switch connecting two 12v batteries. There are three studs on the switch and connected to the bottom stud is a device consisting of a metal strip with a small box and another stud connected to two red cables that supply the power to the boat.

The connection is corroded and I would like to replace it, but I don’t know the name of the electronic part. I think it must be some kind of fuse or protector.In line breaker

Sorry I can’t be more specific, but I haven’t been able to find a name for this part.

Hope you can tell me what this part is.



Hi Larry,

The rusty device is an inline circuit breaker. You can buy a new one from our sister site.

Hope this helps,



Thanks so much for the info. We greatly appreciate your kind help.

Keep up the good work.


Boat Wiring Wizard?


I could really use some of your wiring wizardry.

I have have a 2009 Centurion Avalanche. I put it up for winter and everything was working fine. I charged and installed the boat batteries after winter. All of the switches work, horn, stereo, pump, etc. I go to bump the key and I get nothing. The boat is still on the trailer and before I drag it to the lake I wanted to ensure that power was getting to the starter.

I made sure that the batteries are fully charged, boat battery switch is in the on position, emergency kill switch is in place, boat is in neutral…and I get nothing when I bump the key. I pulled the fuse behind the ignition switch and it looked fine.

The boat has dual batteries. The boat dealer added an marine battery switch last year as the batteries were draining even though the battery switch was turned to the off position.

The boat on has forty hours on it. After working in a confined space and pulling my hair out, I could use some expert advice.



Hi Tommy,

If the instruments have power when you turn on the key, then I would check the neutral safety switch. Based on Standard Boat Wiring Colors, follow the yellow/red wire from the starter post on the key switch to the neutral safety switch in the shifter control.

If the key switch has no power, I would check the breaker on the engine that feeds power to the ignition.

If you use a voltmeter or a test light, you will be able to find the problem. It may be something as simple as wiggle the shifter a little or replacing the starter solenoid.

Hope this helps,



I’m in the boat now with even less hair.

The ignition in the on position does nothing as well as the start position.

It appears that power isn’t getting to the switch. The fuse leading up to the switch looks good. I have also been playing with the shift lever to find the sweet spot, no luck.

Trying to locate the breaker on the engine.

Thanks for all of your advice, hopefully I can get on the lake today.



You the man!!! It was the engine breaker.


Memory Loss

Hello Kevin,

I have a Wellcraft Portofino that I have owned for several years.

When I bought the boat it had an AM/FM CD player in the cockpit that worked fine. I added a car style radio to the salon about three years ago. I wired the unit properly and attached the “memory” lead to an empty, fused position on the same 12 volt bus as the cockpit radio.

From day one the salon radio would lose it’s memory on engine start while the cockpit radio did not. In between engines starts is not a problem. I double checked my wiring, which seemed good and wrote the problem up to buying a cheap radio on sale.

Midway through last season I replaced the cockpit AM/FM radio with a new Sony Marine unit. I now have the same problem with this radio! The tuner memory holds until I start engines. I just don’t get it!

The marine electrical is set up with two battery banks. The starboard bank is a 4-D and starts that engine and navigation equipment including the cockpit Sony radio. The port bank is a bank of four 6 volt deep cycle batteries wired series/parallel for 12 volts that start the port engine and also supplies the house.

I have checked all of the radio connections. I have switched the memory lead from the original fuse panel to different bus bars. Nothing has helped, as soon as I start an engine with the same battery bank the the AM/FM radio memory leads are attached to, the memories go blank.

I am starting to think that this is a surge problem. I believe I have confirmed this by using my master boat battery switches to start engines on the battery bank that does not have the radio memory. If I do that there is no memory loss. Starting and running my boat in this manner is not practical for me and leaves open the possibility of draining the wrong battery bank.

This situation is really starting to drive me nuts, I’d greatly appreciate any recommendations you may have.

Thank you,


Hi Mike,

Stereo memory circuits are sensitive to low voltage and you are suffering for a voltage drop “stack up” and will reset after only a few milliseconds of low voltage. This is very common with newer, higher draw, higher tech stereos.

The power feed to your helm has a drop. The more current that you draw through it, the more the voltage drop in the circuit. When higher draw devices such as bilge blowers, cockpit lights, stereos, the voltage drop is even higher. Slightly corroded connections induce voltage drops. When you start the engine, the source voltage (the battery) drops lower which makes the stereo input voltage that much lower.


  • Increase the size of the power feed wiring and ground to your helm panel.
  • Run a dedicated power and ground lead from the battery to the stereo.
  • Make sure you use circuit protection at the source of power. An increase of 0.1 volts will mean the difference between the stereo memory resetting and remaining.

Hope this helps,