Bow battery? Stern Switch?

Hi Kevin,

I want to add a second battery at the front of my 18 foot pontoon boat to run a trolling motor that will mounted on the front.

I would like the main motor, a 70 hp Evinrude, to charge the trolling motor battery. Battery switch

What gauge of tinned marine wire would you suggest? I assume stranded wire would be best.



Hi Artie,

If you want your 70 hp Evinrude to charge both batteries, it may be easier put the second battery at the stern of the boat and connect them together with a boat battery switch system, which you can find our on sister marine electrical site.

This will allow you to select which battery the engine is starting from and also help prevent a dead battery after too much trolling motor use.

Run the trolling motor leads to the rear of the boat and use circuit protection as close as possible to the battery for the trolling motor.

The cables that connect the batteries are short and there is no requirement to have circuit protection on them since that can be used as part of the starting circuit.

Never use the frame of the boat as the path to ground. It will cause SEVERE galvanic corrosion.

Good luck,


Bot Buddies

Dear Kevin,

Last summer, I purchased a new aluminum fishing boat. It’s great, but I screwed up by “cheaping out” at the last minute. I passed on the trolling motor package and – as you’ve probably guessed – now want to add a trolling motor.

As a long time reader, I know that you are a big fan of Motorguide trolling motors and I’ll be buying one in the next couple weeks. My question concerns the boat wiring.

The Motorguide will be bow mounted, but since I didn’t get the trolling package, the only wire at the bow is a 16 gauge pair for the Attwood LED navigation light. But, according to your boat wiring size calculator, the trolling motor should be wired with 6 gauge.

Is there any way to make the smaller wire work? I hate to start rewiring a brand new boat if I can avoid it.



Hi Sean,

Since your boat is new, you may be in luck. A lot of boat builders now use Ancor’s new Nanotech Wire. As you’d guess from the name, it uses nanotechnology to solve problems just like yours.

Simply put, Nanotech Wire matches wire size to power demand by moving copper to where it is most needed – sort of a Viagra for marine electrical.

In the past, running a trolling motor on undersized wire caused voltage drops, heat buildup and embarrassing insurance claims. But now, that same temperature increase signals Nanotech Wire to deploy an army of nanobots who quickly rebuild the harness to match the power demand. While at work, these little guys make the wire looks like a python that swallowed a large rat.

Once your harness is properly sized, the same bots then go to work on its insulation so that it correctly corresponds to standard boat wiring colors.

The patented process is called Nanotech Overload Sensing Heat Induced Tranference and it works great. The only time I’ve seen it fail is when there are so many accessories turned on that there is no extra copper available. If this happens a lot, I usually recommend the addition of a copper reservoir to supply additional material as needed.

Have an excellent day.


Nautical equivalent of “Old Sparky”

Hi Kevin,

I found your boat wiring website and would be grateful if you might comment on the following for installation of marine electrical systems in an aluminium hull boat. Its a complicated issue I know!

  • AC system includes generator, inverter and marine electrical shore power. The AC system is entirely floating,  i.e., no negative grounding and is interfaced with shore connections via an isolation transformer.
  • DC system includes house battery, engine alternator (isolated negative) and engine battery. All are grounded to one common negative pole on the hull. No other equipment is negative grounded.

I have been told that it would be better to float the DC system entirely as well (same as AC) so that there is no negative ground at all. Is this correct?Shock hazard



Hi Al,

Unless somebody went through and removed the AC/DC ground connection, it should still be intact and must remain. A boat without this connection is an extreme hazard. With an AC fault to the hull, there is no low resistance path back to ground to trip the breaker and the boat will turn into a very large electric chair.

On your boat generator, the AC ground and AC neutral are connected together on the metal engine block of the generator. The generator negative battery cable is also connected to the engine block and your DC negative system. An inventer will have the same AC neutral to AC ground connection. Your AC distribution panel should have a link between the AC ground (Green) and the DC negative on your boat.

Hull ground isolation is nearly impossible on an aluminum boat with an engine and unsafe on an aluminum boat with AC power. The engine and its underwater gear are inevitably electrically connected to the engine block and the DC negative. A positive hull connection to the DC negative gives a low resistance path back to AC ground and DC ground in the event of a fault. A DC fault to an un-grounded hull can create accelerated galvanic corrosion. The area with the positive cable connected to it will corrode to protect your engine and drive.

Hope this helps,


GI Install

Hi Kevin,

I recently received one of the Easy Add AC Shore Power systems from your Boat Wiring Store.

The system looks great…perfect for my Whaler Outrage. But, prior to installation I have a couple of questions. I have a 30 amp Yandina galvanic isolator that I plan to install along with the shore power kit.

Could you give me some idea of how it should be wired? From what I have read on Yandina’s instructions the green wire (ground) on the panel should be connected to the isolator with the other lead from the isolator comnnected to the boat’s 12 volt ground….if so will any ground wire work or do you suggest a dedicated ground wire directly to the house battery?

Thanks beforehand for your assistance.Whaler 220 Outrage



Hi Greg,

The best place to install a galvanic isolator is in the green wire between the ac shore power inlet and the ac panel. This will ensure that there are no alternate paths to dc ground thst can cause galvanic corrosion.

Cut the white jacking back on the shore power inlet where in the desired area. Cut the green wire and install the gi.

Hope this helps,