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Author Topic:   Primary Battery Wiring for Two Batteries; Battery Life, Charging
gmoulder posted 11-18-2013 06:24 AM ET (US)   Profile for gmoulder   Send Email to gmoulder  
Hello. I have several electrical questions about my 1988 Boston Whaler Outrage 18, with twin 1996 Johnson 70-HP engines. The battery circuit is wired per the "new" manner per Jim H. The port engine would not start on its battery, so I switched to BOTH, and it still would not turn until I turned the ignition switch on for the starboard engine. How does this work? I thought that the port engine could "see" the starboard engine battery by moving the switch to "both", why does the ignition need to be on?

A dual bank charger is not charging--at least the lights are not on--and I will get the multimeter out and determine if the lights are not on or if it is, in fact, not charging.

It has been several years since I purchased batteries. How many years do good cranking batteries last? Is there a consensus as to the best--or best three--cranking batteries? If a cranking battery has been completely discharged--I have not taken a reading yet, but not a whimper from the starter--can it be re-charged to full charge? What size or capacity batteries are right for the boat? Generally, I only run the Hummingbird navigation station, very rarely the stereo, and even less rarely the navigation lights. There is no live bait, radar, or anything else.

I want to check the charging output of the port engine. The SELOC manual says to check the terminal voltage with the engine NOT running, and then again Running; and that there should be approximately a 0.3 volt delta with the engine operating. Is that it, or is there more?

This all started with the port remote trim not working. Pulled in a new harness, installed new switch. Now am thinking that it had more to do with not having power from the port battery. It was fun putting the new stuff in and there was a bad wire in the harness anyway. Sure is tight under that console.

As always, thanks, Glen

jimh posted 11-19-2013 10:04 AM ET (US)     Profile for jimh  Send Email to jimh     
The primary power distribution wiring is completely independent of the position of the ignition key switch. If you observed some sort of dependence on the position of the ignition key switch in the distribution of the primary battery power wiring, you have something very odd happening.

The "new" wiring method is shown in an article at

That method was developed as a simple way to utilize just one of the common OFF-1-BOTH-2 switches with twin engine and dual battery installations. The goal was to avoid having the two engine charging systems tied together in normal operation, to have a simple system, and to be able to combine the batteries in parallel for emergency starting.

I do not know that there is any sort of consensus on best battery brand or model for engine starting. Check the engine's owner's manual for the suggested battery capacity for starting. For a 70-HP engine I would expect that a MCA rating of about 700-Amperes would probably be enough. Given the frustration of having a dead battery on a boat when out on the water, I recommend getting a new engine cranking battery every three to five years. Cranking batteries that are discharged to a very low state of charge and allowed to remain in that condition tend to never come all the way back.

Your house loads sound very low, only a few amperes, and you could easily run them from a cranking battery without fear of too much discharge. With two batteries, if the battery running the house loads were to become discharged to the point where it could not crank-over its engine, you could always use the emergency parallel switch setting.

A battery's terminal voltage when not being charged will be 12.6 to 12.9-Volts if at full charge, and less at lower charge states When being charged the terminal voltage should rise to at least 14-Volts, unless you are using a special long-term float charger with excellent voltage regulation; those chargers tend to hold the battery voltage to about 13.5-Volts.

It is common for smaller outboard engines to have little voltage regulation in their battery charging output. They depend on the battery itself to act as a voltage regulator. If those 1996 outboard engines do not have a well-regulated charger, you should probably use a flooded-cell vented battery. That will allow you to replenish the electrolyte if the charging system boils off too much of it during operation.

jimh posted 11-19-2013 10:10 AM ET (US)     Profile for jimh  Send Email to jimh     
Flooded cell lead-acid batteries cannot be shipped with the electrolyte in the battery. As a result they are usually sold through special distribution centers. You can find them at retailers like Sears.

Batteries with absorbed glass mat construction (AGM) can be shipped by the usual methods, and this has made them very popular. I do not recommend an AGM battery unless the outboard charging circuit is well regulated. AGM batteries are typically more expensive than flooded cell batteries of similar capacity.

I like to buy a battery based on the retailer and his presence. Retailers with national distribution like Sears or WALMART can be a good way to buy a battery. Your local boat dealer might have batteries, too.

jimh posted 11-19-2013 10:18 AM ET (US)     Profile for jimh  Send Email to jimh     
Regarding diagnosis of the cause of trouble in systems that run from battery power: it is my experience from about 45-years of working on battery-operated equipment, that the first component to test and verify is the battery.
jimh posted 11-19-2013 10:21 AM ET (US)     Profile for jimh  Send Email to jimh     
Based on your narrative describing the dependence of one engine starting on the position of the ignition key switch for the other engine, it sounds like your electrical system may have joined in common the two ACCY circuits from the ignition key switches. That is not a good practice. The ACCY circuits should only be made into a common circuit with steering diodes. You should check into the wiring more thoroughly to see if someone has created this problem for you by bad wiring.
gmoulder posted 11-20-2013 05:55 PM ET (US)     Profile for gmoulder  Send Email to gmoulder     
Thanks for the information, and for maintaining this great forum where so many Whaler folks get so much enjoyment and help.

More on my problem(s): The engine manual says that the '96 Johnson 70 hp is, among other things, fully regulated. The present batteries (three-year-old to four-year-old) are AGM. The local (Houston) marine repair place recommends Interstate Continental batteries. This weekend promises to be fun with the replacement of the charger and batteries, as well as cleaning up the rat's nest behind the console. While I am at it, will investigate how the Port engine needs the Starboard ignition on to "see" the Starboard battery. Please help me understand your meaning of "ACCY". I will trace the wiring attaching to the two ignition switches. Regarding the primary wiring, I followed your diagram precisely when I rewired several years ago, and it has worked great since.

To the question of how to check the charging condition of the Port engine. If the engine should charge at 14-Volts, and the highest voltage a fully charged battery should indicate is about 13-Volts, then the delta would be about 1-Volt at the terminals when charging. Is the test as simple as testing across the terminals with the engine off, and then again while it is running to see if the 1-Volt delta is developed?

Thanks, Glen

jimh posted 11-20-2013 06:38 PM ET (US)     Profile for jimh  Send Email to jimh     
ACCY is the acronym for accessory, which is the term used to describe what is usually powered by that circuit, that is, accessories of the engine. The ignition switch is usually wired to provide power to the ACCY terminal when the switch is in the RUN or START position.

You should be able to see a 1-Volt increase in the battery terminal voltage when it is being charged, except in the case of the battery already being just about at full charge and the charging voltage being limited. A lead-acid battery will hold a higher than normal terminal voltage immediately after the charging voltage is removed. Allow about an hour for the lead-acid battery terminal voltage to get back to its actual voltage that indicates its charge level. If you measure the resting voltage immediately after removing the charging voltage, the resting voltage will be higher than it will be in about an hour.

jimh posted 11-21-2013 10:21 AM ET (US)     Profile for jimh  Send Email to jimh     
Re-reading your narrative, I found a new possibility that would explain the problem you experienced with getting the Port engine to "turn"; you say the Port engine will not "turn" unless the ignition key switch for the Starboard engine is "turned on". I assume you mean that the Port engine will not crank in the START position of its ignition key switch unless the Starboard engine ignition key switch is set to the RUN or ON position. The most reasonable explanation for this is there is no power being supplied to the Port engine ignition key switch except via the Starboard engine ignition key switch A or I circuit.

Look at the proper wiring of the ignition key switch as I show in my article at

and specifically at the pictorial diagram of the ignition key switch wiring.

You should see that the B terminal of the switch is to be supplied with 12-Volt current from the battery. This usually comes from the outboard engine wiring harness. This circuit is usually fused under the cowling of the outboard engine.

In your narrative you have described a behavior that could occur if the B terminal of the ignition switch for the Port engine were not being supplied with 12-Volts from its usual source, Based on your description of its behavior, it sounds like the source of 12-Volts is from the Starboard ignition key switch and its A or I circuit. This would cause the Port engine to be unable to crank or run unless the Starboard engine ignition key switch were in the ON or RUN position.

gmoulder posted 12-08-2013 07:25 PM ET (US)     Profile for gmoulder  Send Email to gmoulder     
Was finally able to get to the boat today, and confirm that the primary wiring is as it should be [as described in your "new" way]. New Interstates have degraded to about 12.56 volts each from new several weeks ago. Confirmed that STB engine will crank in off, 1 all, and 2. Port only cranks when the STB key is turned on. Want to be in the water for the Kemah boat parade next weekend, and would like to have this business cured by then. Have both ignition switches pulled away from console so can look at both easily. Will check wiring against your graphic first. Any other ideas, realize that it is a matter of checking methodically from here. So many people have had their hands behind my console, I will feel better knowing the story myself after I find the answer. Thanks, Glen
jimh posted 12-09-2013 12:29 AM ET (US)     Profile for jimh  Send Email to jimh     
See my last reply (above) for my most reasonable guess at the cause.
gmoulder posted 12-10-2013 03:30 PM ET (US)     Profile for gmoulder  Send Email to gmoulder     
I can only get to the boat on weekends at this time, and look forward to getting to the end of this puzzle this coming weekend. Am confident that your idea will prove correct. Will bet that something in the chain of electrical supply for the port engine malfunctioned and that someone wired a jumper from the "on" terminal of the starboard ignition switch to the "on" terminal of the port switch. Will confirm this and then work backwards to find the cause. Am not thrilled with all the accessory load going through the starboard switch. If the fix is too difficult to get from the engine, what do you think about pulling power over from the 12v buss to the port switch. Thanks, Glen
P.S. Don't know where you are on the Great Lakes, but was watching some of the Bears / Cowboys game last night and it really looked cold for boating.
gmoulder posted 12-17-2013 09:06 PM ET (US)     Profile for gmoulder  Send Email to gmoulder     
Am creeping up on my wiring issues. This past weekend made some improvements to the general wiring inside the console. Discovered that the port ignition fuse had blown, and in that condition, the port engine could be started if the starboard ignition was "on". Using your ignition switch wiring diagram, and the digital multi-meter, determined several things: apparent voltage leaks within the port switch, and that there are mystery connections within the wiring of the two engines associated with the ignition switch. Should have two new switches this weekend, and plan to rewire the ignitions using your switch wiring diagram. I believe that starting at the harness and wiring per the single-line should resolve whatever jury rigging was done. I would like your advice on the wires going away from the switch to users: there are accessory power leads and grounds which serve multiple lamps and other from a single lead and terminal. Do you set up distribution busses or use a butt-connector which will accept two or more leads on one side and doubling the single lead on the other side? Surely appreciate your help. Glen
jimh posted 12-17-2013 11:46 PM ET (US)     Profile for jimh  Send Email to jimh     
I recently refurbished the secondary power distribution on my 1990 Boston Whaler boat. I described the changes in

I don't have a photograph of the wiring to the fuse panel. I retained much of the original power distribution wiring, and this constrained the arrangement of the conductors at the panel. That is one way to say that the installation is not in the category of being an objet d'art. It is a very functional installation, but it won't win any prize for using the most nylon ty-wraps or having the most wires bent at exactly 90-degrees.

gmoulder posted 12-20-2013 09:41 AM ET (US)     Profile for gmoulder  Send Email to gmoulder     
This message should be my last request for help on this subject, as I want to complete the re-wiring this weekend. After reading all your information on the subject several times, it occurs to me that there will numerous keyed power and ground leads to users, particularly gauge lamps. Am thinking to install a distribution board and route all the keyed accessory power and ground leads to that board, and then have a single lead for each to the port or starboard ignition; again, I have 2 each 70hp engines. This method will be much easier and cleaner that wiring 2 boards with leads to the 2 separate switches. Not trying to dodge work, but I can't see any reason [other than perhaps overloading the single switch] to not proceed this way. What do you think about this? Again, thanks very much for your help. Glen
jimh posted 12-20-2013 10:46 AM ET (US)     Profile for jimh  Send Email to jimh     
Glen--First, don't worry about posting too many questions. You are welcome to post as many times and as often as you like.

Re gauge illumination circuits: these are often daisy-chained from gauge to gauge by running a conductor (with BLUE insulation) from one lamp circuit to the next. You could run individual conductors from each gauge to a bus, and then power the bus from a switch. On most Boston Whaler boats that have a compass there typically will be a switched circuit for the compass lighting. You can use that circuit for the gauge illumination.

The switched 12-VDC that comes from the ignition key switch is usually on a conductor with insulation of VIOLET color. This indicates a source of power that follows the engine power. You can also use a small bus to distribute that power to various devices. (I do this on my boat. The switched 12-VDC power is taken to a small bus, then a few devices are connected to the bus. One of the devices is an hour meter.)

The negative circuit is typically in common for all devices, so you just need on large bus with plenty of space for all the negative connections. You could also, as you suggest, create some tertiary negative buses and connect some devices to those tertiary negative distribution circuit, with that bus being connected back to the secondary negative bus on your helm power panel.

With twin engines it is sometimes seen that the switched 12-VDC (VIOLET) circuits will be combined by using two steering diodes to create a third circuit. This third circuit will have 12-VDC power when either of the engine ignition keys are set to ON. The only drawback to this circuit is the slight voltage drop across the steering diodes. You do not want to combine the two engines' switched 12-VDC circuits without the diodes, however, as that will place them completely in common. That is probably not a good practice. (I think you might have something like that going on now on your boat.)

jimh posted 12-20-2013 10:54 AM ET (US)     Profile for jimh  Send Email to jimh     
If you want to make a daisy-chain distribution of the VIOLET or BLUE conductors at the gauges, I would make the daisy-chain with short lengths of wire with ring terminals at each end. You'd have two ring terminals under the wiring post at each gauge.
gmoulder posted 12-23-2013 10:05 PM ET (US)     Profile for gmoulder  Send Email to gmoulder     
The saga continues. This weekend, I spent about 7 hours outside (and it is cold in Houston) working on the wiring. Once I took the gauge panels off and saw the wiring, I am surprised that the boat ever ran and that I did not have a fire onboard. There were strings of red leads running away from gauges attached to a brass machine screw from which ran strings of green leads running to I don't remember where, all tied together with the machine screw wrapped in black tape. There were several of these businesses. Working one circuit at a time, I removed the crazy wiring, mostly by daisy chaining the power and ground leads to lamps in the gauges. Some of the confusion was 5 times too much wire stuffed into balls. Installed the two new ignition switches. Hoped that it was going to be only following the connection pattern of the old switch to connect the wiring harness wiring to the new switch. No such luck. The new switches have a slightly different layout from the old. Did my best, but when it came to the smoke test, the port engine started on ON or RUN not START and the starboard engine did not turn over, although there is power to the switch. The attaching of the wiring harness leads to the switch seemed straight forward, but something went wrong. I am going to invest time this week understanding what is going on inside the switch, and more hours on the boat (starting fresh) dealing with the switches. These switches say to run the ground to the raised M terminal and the magneto to the lower M terminal; I imagine that the idea of going to the upper M with the magneto is to mitigate any arcing. I really do not want to give up and take the boat to the repair person as it has become a personal thing (man vs switch). I am an ME and build large industrial plants for a living, so single line drawings are not a black art for me. I ought to be able to lick this. Any tips would be appreciated. Thanks, Glen
jimh posted 12-24-2013 12:01 AM ET (US)     Profile for jimh  Send Email to jimh     
Let me reply in small increments.

Re the M terminal that is raised: I would have thought you'd put the high-voltage lead from the engine onto this terminal. And put the ground on the lower M terminal. That is what I have recommended in my article on ignition switch wiring. See

That arrangement is based on the OMC and later BRP recommendations. They make sense to me. You want the terminal with the most voltage to be the raised or elevated terminal so you get that circuit away from the others.

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