Easy Ac/Dc

Easy Ac/Dc serves as a forum for the discussion of boat wiring concepts, products and issues - many of which are generated by reader’s questions.

If you have a boat wiring issue that you would like us to tackle, please send us an email at kevin@easyacdc.com.

You are also welcome to browse the existing posts and add your comments to any articles that you like.

Or, if you’re trying to track down info about a more specific category, please use the search box in the upper right of this page or check out the list of various subjects on the right side of this page.

Again, we welcome your questions and suggestions relating to new topics as well. Please send us your ideas for boat wiring topics that you would like us to address.

We hope that you enjoy your visit here. Please come back often.

Hi Kevin,

I have a powercat with twin 115 outboards and two batteries, one for each motor.

I am looking for the simplest way to connect the two batteries in the event one goes dead (ie: one engine has a problem starting and its battery gets drained trying to start it). Right now I carry jumper cables to do this if necessary, but I am looking for a built in system.
Can I just connect the positive of both batteries through a battery switch, and then if I need them to be joined just close the switch?

Thanks!

Jonny

Jonny,

The simplest way to connect your two batteries is with a battery switch between the positive of both batteries. Make sure you the negatives of both batteries are also connected together. This connection should be constant and not have a switch.

Another option is an emergency paralleling VSR. This device connects between the two positive battery posts but provides automatic cross charging of both batteries along with a manual and remote emergency paralleling feature.

When operated remotely, a momentary (horn style) button is pressed once. The emergency parallel switch connects the two batteries for 10 minutes. If the battery voltage is not above 13.7 volts after 10 minutes, the switch opens the circuit. If the voltage is above 13.7 volts, the connection between the two batteries remains and allows the alternators to completely charge both batteries.

Hope this helps,

Kevin

Kevin!

Thanks for the response! I guess what I was wondering is, if I could get away with only connecting - through a battery switch - the positives of both batteries to join them?

Since each battery is grounded to it’s separate motor, I suppose I would need to have them additionally on a common ground buss (permanent) as well?

The VSR looks like a perfect solution as well!

Thanks again for your help!!!

Aloha,

Jonny

Jonny,

If you connect the positives together for starting, you need to connect the negatives together to complete the circuit.

There will be some circuit in your boat wiring that connects the two grounds together. This wire will attempt to carry the starting current of your engine. Usually, the smallest wire (quickest to burn) that connects the two grounding systems is the ground wire between your gauges. The engine would attempt to start. To complete the circuit, the starting current would attempt to flow through the 16AWG ground wire between your gauges. This usually causes a fire.

Let me know if you have any other questions,

Kevin

Kevin -

Your website is fantastic, but I could not find any information on my issue. I am relatively new to boating and know very little about electrical systems. I have a 2006 Bayliner 175 with a 135 Mercrusier Alpha I.
My issue is that the blower will not turn on when I flip the switch at the helm. The indicator light comes on but no blower. The previous owner, a friend of mine, said he had some issues with the blower being a bit delayed (5 seconds or so) when he had the boat. Now it will not turn on at all.

I’ve narrowed it down to four potential problems:

1. The blower itself does not work. In that case I could just replace it but want to avoid having to take it out (it’s relatively difficult to get to).
2. The switch has gone bad. I did, however, disconnect the two wires coming to the switch and touched them together. The light came on but no blower so I figure that is not the case.
3. The fuse. I checked it and it looks fine. Although when I pulled it out and replaced it, the indicator light would not come on at first. Eventually, it did. Since the light comes on I figure the fuse is ok.
4. The boat wiring. The problem is that I have no idea how the boat is wired OR how to run new boat wiring if necessary (i.e. from the battery to what, and then the fuse? or switch? or blower?). On this I am totally clueless on how to complete a circuit, especially when the existing wiring runs through the engine harness, fuse box, etc.

Any help you could give (especially on #4) would be a huge help.

Thanks!

Frank

Frank,

A non-operating blower could be a real hazard.

Most boat wiring problems occur at connection points. Most delays in DC devices are caused by bad connections.

Positive portion of blower circuit - usually yellow wire

• The blower switch gets power from the fuse panel.
• The next wire in the system runs for the switch to a multi-position wire connector connecting your helm switch panel to the main boat wiring harness.
• The next wire in the system is in main harness between this multi-position and the blower.

Check all of these connection points.

Negative portion of the blower circuit - usually black

The negative system is simple. It should run from the negative of the blower, through the main harness, and to a ground buss. Sometimes this buss in on the engine, sometimes mounted on the transom, and sometimes the negative post of the battery is used.

Check all of these connection points.

If you do not find a bad connection, you will need to remove the blower. If removing the blower is nearly impossible, disconnect the wiring at the blower and connect something of similar current draw to the wires to test the circuit. (Bilge pump, 24W light, etc) If your test item works correctly and doesn’t have a delay, I would replace the blower.

Finally, since this is a job that you won’t want to repeat, consider getting a long life blower. My choice would be an Attwood blower. No one builds them better.

Hope this helps,

Kevin

Hey there-

I am looking for an engine wiring list of colors for an inboard 350 on a 1972 correct craft.

I bought the boat from a guy who got tired of his project. It has a new engine and a new wiring harness, but no gauges. The harness has two parts. One part that is to be wired to the engine and had a large round plug on the other end. The other part is the part that goes to the dash. It has the female large round plug and on the other end of it it has a square plug for the dash. The dash plug looks like a flat trailer plug with an extra row on top of it in for a total of eight wires.
Anyway, my question is, that colors go to what?
Here is what I have:

• Large Red wire w/ purple stripe
• Large black wire - probably to ground.
• Purple wire
• Baby blue wire
• Yellow wire w/ red stripe
• Brown wire with white stripe
• Tan wire with blue stripe
• Grey wire
• Tan wire

Can you tell where on the engine these wires go? I have no old reference as this is a new block and the boat has been stripped.

Thanks in advance for your help!

Mike

Hi Mike,

See below for the standard boat wiring colors.

Please let me know if you have any other questions,

Kevin

Large Red wire w/ purple stripe
Helm power in fed from 50 amp breaker on engine
Large black wire - Probably to ground
Helm ground wire - connected to engine ground
Purple wire
Ignition power from key switch - powers instruments and coil on engine
Baby blue wire
Oil pressure - sender on back of engine just behind distributor
Yellow wire w/ red stripe
Engine start - usually runs through shifter for start in gear protection and continues to starter
Brown wire with white stripe
Power trim sender wire - might be some other wire on your inboard
Tan wire with blue stripe
Engine alarm
Grey wire
Tach signal - usually connects to negative side of coil
Tan wire
Water temperature - usually connects to water temp sensor on intake manifold near thermostat housing

Hi Kevin,

I just bought a 1986 19.5 foot Bayliner Capri, and am loving it. One of my first priorities is to get the navigation lights working so I can use it at night.

Here’s what I know:

• The switch at the dashboard is missing.
• The wires coming out from the front light are solid black and solid white. But I don’t see them back at the dashboard.

Assuming that I can find or pull wires, I’m guessing, based on what I have read on your site, that I need to be able to turn on just the light in back (on a pole) or just the red/green light (in front).

If I get all the wires fished through to the dashboard, I’m going to tie the grounds together to a good known ground, and then get a two-way switch that will switch power into one or both of the positive wires to the light?

Any thoughts or advice would be great.

Thanks very much.

Evan

Evan,

You will want to use a dual pole, dual throw switch to control your anchor and navigation lights. When the switch is in the navigation position, you want the red/green light and the white stern light to be on. When the switch is in the anchor position, you want only the white stern light to be on.

From the front, this will be a three position switch, ON-OFF-ON. From the rear, this switch will have six terminals. (It may have seven if there are any lights in the switch)

From the back, this switch will appear to have three rows of terminals with two terminals on each row.

From the back, here are your electrical connections

• Top row left - no connection
• Top row right - white stern light and short jumper wire
• Middle row left - 12 + power
• Middle row right - 12 + power
• Bottom row left - red/green bow light
• Bottom row right - short jumper wire that is connected to the top row right terminal

If your new switch has a 7th terminal on the top right, connect a ground wire to this to activate the lights in the switch.

Hope this helps,

Kevin

Hi Kevin-
I finally got around to wiring in the nav lights, and everything worked perfectly when I bought the switch and wired it up as you described. (Although I’d love to find the guy who mounted the fusebox in that impossible to see location…)

However, the fuse kept blowing… the ones I had handy were 2 amp and 1.5 amp (both blew). That seemed small, so I checked the owner’s manual, which didn’t specify a fuse size.

I have read that you calculate the fuse size by the load, so I’ve got the stern light bulb, the anchor light bulb and 5 small instrument lights, and the wire is 16 gauge I think, but I’m not sure of the total watt load.

Anyway, short version of the question is: what size fuse should I use?

Thanks very much for your help on this… (The boat is a 1985 bayliner capri bowrider)…

Evan

Evan,

The 2 amp may have been adequate for the navigation lights only. The instrument lights caused the fuse to blow.

You can certainly use a 5 amp fuse for your navigation light circuit. If needed, 16 AWG can easily handle 10 amps.

Glad to help,

Kevin

Hi Kevin,

I want to install switches for my bilge pump and a seperate one for my lights as well as one for my livewell - everything will be pluged in at rear of the boat.

I need to know how to plug it all together. It’s a 16 foot outboard. I’m confused on how to connect the three switches and then to the battery.

Phillip

Phillip,

The simplest solution would be to purchase one of the pre-assembled boat wiring harness and marine electrical panel sets that are available at EzAcDc. These are really well thought out parts that simply snap together.

A good choice for your boat might be their basic Small Boat Wiring Harness that is designed for a boat with the switches in the rear. It provides wires for bow and stern navigation lights, bilge pump (manual and auto wiring), and livewell pump. This harness connects directly to your boat’s battery (through the provided circuit breaker).

It plugs directly to the Fully Wired Fishing Boat Panel. This panel provides switches and circuit breakers for your bilge pump, navigation lights, livewell pump, and an accessory.

EzAcDc has bilge pumps, livewell pumps, and navigation lights that plug into the waterproof connectors provided on their harnesses. They provide adaptors for all connections if you are using your legacy components.

Hope this helps,

Kevin

Kevin

The ignition switch on my boat went bad over the weekend.

I disassembled the dash and I forgot to mark the wires and where they were connected to the switch. It was a 4 prong switch.

I visited my local marina and the owner told me I can use a 3 prong. Is that true? Can you guide me as to which wires are connected to which prong?

The boat is powered by a 5.7 Mercruiser Alpha 1 Gen 2, No EFI, Carb. I do have an Accessory switch on my dash that I use that to power the radio. The lights have there own seperate switches. So I believe that there is not an accessory connection wire on the ignition, I could be wrong?

Needs Help in NY

Ray

Ray,

You can certainly use a 3 prong switch in place of your 4 prong.

Here are the standard connections and their colors:

• B post - Battery - red or red/purple
• S post - Starter - yellow/red
• I post - Ignition - purple

Please let me know if you have different color wires for your ignition switch,

Kevin

Kevin,

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.

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.

Dave

Dave,

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,

Kevin

Hi Kevin,

I recently purchased a boat wiring harness, marine electrical panel, battery switch and VSR from EzAcDc. These are for my boat’s two battery system in which my trolling motor batteries are separate.

• What are the best batteries to use for this system? Auto starting, marine or deep cycle?
• On the switch are four bolts, Is it important to put the positive leads from battery, VSR, engine cable and neg lead to bus on certain bolts?
• And do I need to put a fuse on each positive lead going to the batteries?

Thanks,

John

John,

Here is a simple schematic for wiring your boat’s battery switch system.

The most important part to remember on the battery switch wiring is that this switch is basically two ON/OFF switches. Keep the engine side on one set of posts (1 and 1) and the house side on the other set of posts (2 and 2).

In operation, you will turn the switch to ON while running and OFF when you leave the boat. Only use the COMBINE in an emergency start situation.

Battery recommendations
I would use a starting battery for the engine and a deep cycle for the house. Most “Marine” batteries are just a cross between a starting and a deep cycle.

Fuses
You do not need fuses in the battery cables between the switch and the batteries. All other continuously energized boat wiring (accessory harnesses, bilge pump, stereo, etc) is required to have circuit protection.

Please let me know if you have any other questions,

Kevin

Kevin,

Just read this fantastic article.

I am in an “almost” indentical situation where I have a 24 foot Scout Bay Boat, but it has two starting batteries (12 volt starting system) and two trolling batteries (24 volt trolling system) . Can I use the BEP VSR the same way?

I currently have a two-way switch for the starting batteries. Could I still use one BEP VSR and connect it to one of the starting batteries and one of the trolling so the engine (Yamaha 250hpdi) charges all four while underway? If I left the switch on “all” for the starting batteries would it still read the battery voltage correctly and do the switching?

I also have an on-board four battery charger (just an fyi) that does great for on-land charging but I use the trolling motor HEAVY and if I could get some extra juice off the engine it would be awesome.

Please let me know… I’ll by a VSR or whatever I need ASAP (I have a tournament in 2 weeks).

Thanks for the great article and any help you can provide.

Thanks,
Jimmy

Jimmy,

In that article, the boat owner was trying to charge all 3 batteries with a battery charger.

The 24 volt VSR is the appropriate part if you want to charge all 4 batteries while under way. Here’s a good link to check out.

If you leave your battery switch in the ALL position and connect a 24 volt VSR, you will be able to charge all four batteries while underway. Don’t forget circuit protection as close as possible to every positive battery connection.

Let me know if you have more questions,

Kevin