Wiring Starter Battery to Outboard Motor

Hi all, first time poster. I have enjoyed all of the great topics and tips on this forum, especially since I'm doing a complete rebuild of my 1987 Bass Tracker v16 Guide Special. It was a tiller drive model and I have converted it to a console drive. I also upgraded the engine from an Evinrude 15 hp electric start tiller drive to a 40 hp Mercury Tracker console drive. This leads to the question I am posting and need feedback on.

The engine I purchased is a model # 1040312pt Mercury Tracker 40 hp. It has a non-power trim and it does not have an alternator on board. I have purchased the appropriate remote control box (Mercury Quicksilver model 881170A3 side mount control) and have both engine and control mounted on the boat. I am now on the wiring phase and I am a bit stuck on getting power to the starter for the engine. I am used to my Evinrude which had a battery cable integral to the engine which I would just attach directly to the starting battery. I am unclear how the starting battery is connected to the Mercury. In all the wiring schematics I have seen (and I have the newwiremarine.com schematics and wiring guide) they show a positive and negative wire going to the engine. But I also read in somebody's post recently that if you don't have an alternator you do need to run battery wires directly to the engine. So my question is, how does the battery connect to the starter and/or ignition to start the engine? Does it go to the remote control box or directly to the engine? I read the instructions for the remote control and nowhere does it mention power. I am assuming that the with the cable harness from the remote control box routing to the engine, that the power should go directly to the engine, but I cannot figure out where it would connect. Any assistance or guidance on this would be greatly appreciated!

If that 40hp OB is indeed electric start ... I find it hard to believe it came without cables or a harness equipped.

What was this, a private sale? How did they start it before you bought it?

Hi Dale, yes it was a private sale. I checked with Mercury online via the motor serial number and it is indeed an electric start (confirmed by seller). There is a male wiring harness from the control box (which includes a keyed ignition switch) to the engine and the engine has the female receptacle to plug the harness into. I was expecting to see either a battery cable or clear posts on the motor to connect battery wires to, but I don't see either (doesn't mean they are not there!). I will probably end up contacting a Mercury tech specialist, I was just hoping someone on this forum might have some insight on this.

Thanks

Tom (tango66)

Mercury 40hp Electric Start
https://www.marineengine.com/boat-forum/showthread.php?410431-Mercury-40Hp-Electric-Starter-Wiring-Diagram

Mercury Wiring Diagrams
https://maxrules.com/mercwireindex.html

I believe I may still have a PDF of the OEM Factory Service Manual for a mid-90s Mercury 40hp OB at home, if no one else here helps you out.

... I’m still STUNNED someone would sell such a beast and rob the cables off it. You’ll likely need 4AWG cables if there are no longer than 10’ long, but your manual will tell you exactly what you need for battery cable size and for cranking amps (CCA) in the battery.

You can buy an original OEM Factory Service manual online in PDF format for only $12-$20 you know, thus I strongly urge you to buy on for your new motor. This Mercury setup picture below may NOT represent your model ... is just an example.

Power should go directly from the battery to the starter. I have a 91 mercury 25 so may be different. Can you take some pics of the starter? The wire posts are there, likely just camouflaged.

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DaleH said:

ry Service manual online in PDF format for only $12-$20 you know, thus I strongly urge you to buy on for your new motor. This Mercury setup picture below may NOT represent your model ... is just an example.

Click to expand...

Where can I find these? All I can find are the Seloc manuals and they are like $35 online. OEM would be ideal.

Here are a few pics from both sides of the motor. Not sure if these are clear enough to tell. Thanks for any feedback.

I've been reviewing this issue for my old OMC 28 HP. The red starter lead must come from a solenoid (I don't see it) and the starter ground wire (for your starter) needs to be it's own separate line (unlike a car, no chassis ground). Your control (starter and ignition kill switch and maybe choke) wiring will be separate and likely run to that plug I see in your pic. Your (boat side) plug perhaps stayed with the boat your engine came from. Personally I'd be looking on eBay for it.

The negative starter cable lead from the battery should go directly to the starter motor. The positive lead from the battery should go directly to the start solenoid. Then there will be a jumper from the other side of the solenoid to the starter motor positive. The solenoid will have a 12v switched signal wire that actuates it and is controlled by the key switch. There should be another wire for constant 12v power coming off the solenoid where the positive cable from the battery connects to the solenoid.

You have one battery cable connected to the starter - looks like the ground. Where does the other end of that lead go? You will definitely require battery cables directly from the engine to the battery. All that goes through the fwd controls is low amperage 12V to act as signals. Any more pictures of what may be the starter solenoid?