Outboard Wiring

[Hartley18]

Greetings all! This is my first post here.

Our little TS has a 1980's vintage Johnson 7.5hp outboard with a 3-pin alternator connection. When I bought the boat, 2 wires were connected to the AC pins of a (rather rusty) diode rectifier, with the +ve and -ve connected directly to the battery via a 5A fuse, but it doesn't seem to be charging the battery. I've checked the obvious and, no, the fuse is not blown.

Anyone know what sort of voltage/current I should be getting out of this set-up? What should I be looking for to trace the problem? Is this the right way to charge the battery?

I was told that I could get more amps out of it if I hooked up all 3 wires. Can anyone tell me how??

Any advice you can offer would be greatly appreciated!!! Thanks in advance.

[Hartley18]

H'okay, it's been a few days and I now have less of a clue than before...

I know 'red' is +ve and 'black' is negative, but I've got three very identical-looking yellow wires in one hand (no markings at all) and no amount of Googling or searching here gets me any closer to how best to hook them up or to even check it's working when I do!!

I'm sure it's a common problem. Sails I can handle (they go up on this long thing an' the wind blows...), but even though this chunk of metal is the same color, it's getting very close to being used as a single-use anchor next trip.

Anyone have any ideas or can give me a headstart?? Thanks.

[Lancer28]

I can help. Those little johnson alternators can burn out quick and without notice. I have a book here on your outboard, let me peek at it hang on.

[Lancer28]

give me the year of your engine and I'll scan the wiring diagram and send it to you or post it here.

You should check the output terminals on the alternator with a voltmeter to see what volts you're producing at about 30% throttle. Then move back to the rectifier and check that.

Of course, make sure you do the "no-brainers" like clean and protect the corroded connections, check and clean the battery terminals, and make sure you're not drawing more power on your boat than the alternator can supply.

As far as hooking them up, you should have four things: Ground, red which is power from your alternator to the rectifier, yellow for a "sense voltage", and a fourth wire to "excite" the coils. This last wire can have a lamp in series which would light when the alternator is bad because the wire grounds after the coils excite and start making power.

hope that helps. let me know about the year and whether or not you've got electric start.

[Hartley18]

give me the year of your engine and I'll scan the wiring diagram and send it to you or post it here.

Lancer, it's a 1981 pull-start. There's a 3-pin plug on the side of the cowl that seems to disappear up near the top of the motor under the pull-start thingy.

Unfortunately I'm new to outboard maintenance having worked my way up through sailing dinghys. I can look after my car okay (since everything routinely needed is clearly marked), and I've used outboards since I was a kid, but I can't even locate the fuel filter on this thing!

A wiring diagram would be wonderful. What sort of volts should I be getting on the output terminals (when I find them)? AC or DC?? Thanks for your help!

--Cameron

[Hartley18]

We took the boat for a spin on the weekend to check out all my modifications (nearly every weekend over winter!) - some of which worked great (new cabin locker) and some of which didn't (masthead light plug lead 6" too short).

With a fresh batch of fuel the outboard started up and ran very sweetly (thanks to many for their advice ), and I took a few readings on my multimeter at the end of the outboard cable at fast idle:

Orange wire 1 - 2: ~12VAC
Orange wire 2 - 3: ~4VAC
Orange wire 1 - 3: ~9VAC

I just assumed it was AC but these readings were jumping around everywhere, so I'm not really sure. I then plugged the wires into the rectifier thingy (best guess of which leads were which) and measured 19.9VDC between Red & Black without the battery connected. Is this ok??

I then stopped the motor and plugged the battery in (reading a bit low at 11.6VDC), started back up again and away we went 'cause others wanted to use the jetty and my wife was keen to get out for a sail.

I don't have an ammeter so I don't know if its charging or not, but there were no sizzling sounds or smoke coming out of the cabin..

Anyone know what else I should look for??

Thanks,
--Cameron

[capngregg]

With the battery hooked up to the system and the motor running at 30% power or so, you should turn your multimeter function switch to the VDC (or a scale that will display in the 0 to 20 V range) since this is a 12 V system. Connect the meter leads to the battery terminals with Red to the + terminal and Black to the - terminal.

If the system is charging and the battery is in fair shape, you should read something above 12 v with no load on the battery. (lights, etc.) most likely you will read 13.5 v or above. If you're reading something in the 16V plus range you should have the battery tested for condition. If the battery checks okay, the rectifier is probably not operating properly.

Any automotive store (including Sears) will usually check the draw down condition of the battery free.

Hope this helps.

[Hartley18]

Thanks, capngregg - that is most helpful.

I will give it a try this weekend after the in-laws leave.

--Cameron

[capngregg]

OOPS!

I forgot to mention if the battery voltage does not increase over nominal (11.6 V? I think you said) then the alternator is probably not putting out anything.

[Hartley18]

Originally Posted by capngregg

OOPS!

I forgot to mention if the battery voltage does not increase over nominal (11.6 V? I think you said) then the alternator is probably not putting out anything.

I finally got to check this out over this last weekend.

With the motor idling I get nominal volts, but if I rev up to about half throttle I get around 13-13.5 Volts (speed dependent), so the rectifier set-up I've got seems to be working although I guess I'll never understand how.

I'm a bit surprised that the motor is not charging the batteries at idle, but maybe this is normal?

Anyways, thanks for your help.

--Cameron