Sierra 18-5957 alternator wiring diagram??

Ok so on the alternator issue I was having..

I pulled the alternator (on my 78 ski nautique) to bring it to a starter/alternator shop I know of and have it tested. I brought it in and they told me it was putting out nothing. Of course, before i had handed it to the guy I knew it was going to be replaced after seeing "Motorcraft" on the arm of the Alternator. I'm pretty sure thats automotive and should not be in my boat motor.

So anyways, I digress.. I would post pictures but the site is saying "access denied" when i try to upload the pictures.

It looks like it's still wired with the external voltage regulator because it has this little silver box with 3 wires going to it. One of them goes to the alternator. Apparently it was using this old automotive alternator though that is not working now.

I called the Nautique Dealer in my area which is Traverse City MI and the service department said to upgrade to the Sierra 18-5957, 68 AMP Marine Alternator. So I found one on the internet and it is now here. Only problem is, it came with no wiring diagram and I have no idea what to connect the wires to. Two are obvious (Bat. and a ground terminal) but a red and black wire coming from a black plastic box on the alternator, I have no idea.

My old alternator had 4 wires..
A large battery line going to the solenoid+.
An orange wire going to some sort of metal clip on the round choke assembly of the carburetor.
A Blue wire going to the external voltage regulator.
A Grey wire grounding to the engine frame.

Assuming this new alternator is internally regulated, I assume I don't need the blue wire going to the external voltage regulator.


Long story short, I could use help here folks!

Looks like a great Marine Alternator though so i'm looking forward to getting it in and working. I will post pictures in the comments if I can.

This is the million dollar question..

what do i do with the black and red wires??

I actually figured it out my self...


I am quite sure it was the red wire that is the "exciter wire" and gets the charge to the coil in the alternator from the + on the ignition coil. The Black wire goes to the battery + (or actually the starter +) as a sense wire so the alternator can sense the charge level of the system and regulate charge voltage output based on battery condition/demand.

I am pretty sure that is how it is.. I am 100% positive of the function. I never did get the diagram and just asked a marine mechanic near me what the wires were probably for and he told me. I wired it the way he told me to and it's been great ever since.


I will confirm tomorrow when i look at the boat if it's the opposite but I'm pretty sure Red = EXCITER and Black = Sense wire.