Boat Wiring Help and Advice

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Boat Battery Wiring Size


I’m in the process of installing the automatic smart boat battery switch that you designed for EzAcDc Marine Electrical.

On your boat wiring diagram it shows that the boat battery wiring coming from the batteries to the marine battery switch, are 2 AWG ( red & black). The wires coming from the switch to the VSR are 8 AWG.

The cable from my motor, a 50 HP Mercury, are 6 AWG.

Do I use the size wires as shown, or can I use a 6 AWG throughout the complete wiring ?

Will it still work safely ?



Hi Rob,

As you increase the boat battery cable length, you will need to increase the boat battery wiring size to reduce voltage drop.

Mercury provided 6AWG cables with your motor with the assumption that it would be connected directly to a battery or to a boat battery switch with minimal voltage drop. If you use 6 AWG cables from the marine battery switch to the batteries, you will induce a larger voltage drop and may cause your engine to not start.

Running 2 AWG from the batteries to the switch will help reduce the voltage drop to the engine. Another option would be to run 4 AWG from the engine to the battery switch and 4 AWG from the switch to the batteries.

Hope this helps,


Which wire?

Dear Kevin,

I am installing an hourmeter on my 26′ Sunchaser with a 200 HP Yamaha engine.

The positive side of the meter is supposed to be wired into the ignition circuit that has 4 wires, i.e. red, blue, green and yellow. As I only want the meter to function when the engine is turned on, how should I connect the boat wiring? Which wire do I attach to? I think it is the yellow one.Hourmeter

Thank you,


Hi Arthur,

The easiest way to answer your question is either with a dc meter or test light. Test each wire individually to determine which one is the switched power when the key is turned on.

My best guess would be yellow, but use a meter to be sure.


One Size Fits All?


I have to redo all of my boat wiring and was wondering if I could simply use one size (gauge) of wire to simplify the process?And, if so what size is recommended?



Hi Mike,

The wire size depends on the complexity of your boat.

If the boat is small and you only have a set of navigation lights, you could probably wire the entire boat with 14 awg wire.

But, if you boat has several DC devices, you would need to have a larger wire to supply power to your DC distribution system. It would not make financial sense to use this same large wire to for your branch circuits.

I would recommend using our boat wiring size calculator to determine which wire size is best for your boat.

Hope this helps,


The turn of the screw


I am trying to install a new dual trumpet electric boat horn to replace my non-working single trumpet air horn. Have mounted the horn on my pontoon hardtop and used the heavy gauge boat wiring from the compressor to power the horn.

I have approx 12.5 volts at the horn but get only a sound like it’s attempting to blow. I had a similar sound on another boat that had corroded points in the horn. Cleaning these fixed that problem but not on this horn.

So far, I have connected the horn directly to a “jump start” and it works fine…replaced the horn switch…have tried alternate boat wiring with red going to a hot buss bar used by other equipment and black going to a ground bus bar used by other equipment, but all with no results.

Finally, I have checked polarity on the trumpets wiring and colors match

Ever had a problem like this?Marinco dual trumpet electric boat horn


Hi Don,

Some electric trumpet horns are very voltage sensitive. On the back of the horn cover there is usually a sticker that says “AFI” or “Ongaro”. Under this sticker is a small phillips screw. If all connections are good and the wire is the appropriate size, turn the screw until the horn sounds. Usually you loosen the screw, but not always. I would not turn it more than a couple turns.

Hope this helps,



You can’t imagine how many people I’ve asked to look at this issue. Two of them were even marine electrical guys, but no one came up with this solution.

Horn works fine now.

Thanks for the help