Mercruiser 470 3-wire alternator wiring question

Mercruiser 470 (Converted to a 1-wire alternator from a Merc 165 6-Cyl)

I did a search and found minimal results on this topic so I figured I'd see what advice is out there from folks who've done this already. My current alternator is questionable - it has recently been putting out low voltage and the bearings are starting to fail inside. So, I ordered a Delco 3-wire. I understand that the battery sense wire can be hooked to the large output terminal, so unless that is incorrect-that is what I plan to do.

The wire I am a little bit unsure of is the ignition wire. My boat is old - doesn't have a battery/charge lamp, and I'm not sure if I need to use a diode or anything. I guess I'd put it on any switched +12 source, maybe electric choke. Any suggestions?

Re: Mercruiser 470 3-wire alternator wiring question

does this pic help?
(Photo from Don S)

Re: Mercruiser 470 3-wire alternator wiring question

dn010 said:

.... I guess I'd put it on any switched +12 source, maybe electric choke.

Click to expand...

Perfect!

Re: Mercruiser 470 3-wire alternator wiring question

Thanks guys, I appreciate the posts - helped out a lot!

Re: Mercruiser 470 3-wire alternator wiring question

The alternator came with black wire, orange wire and of course the + terminal. I wired the orange to the + terminal, the black to the choke and now my engine runs with the key off. After some research, I have a 2 position ignition switch - not a 3 position like newer boats. Is this correct or is the diode in my alternator bad already? It charges fine, just can't get it to shut off. If the alternator is fine I'll buy a diode and install - can anyone tell me what one to buy? Thanks for any help!

Re: Mercruiser 470 3-wire alternator wiring question

I would guess that you are feeding 12v back to the system through the choke wire. Check it.

Re: Mercruiser 470 3-wire alternator wiring question

Post a picture of your wiring on the back of the alternator.

Explain your 2 position switch. A 3 position is off, on, start.

Re: Mercruiser 470 3-wire alternator wiring question

Is your alternator brand new or rebuilt. Ive seen some rebuilt ones have issues out of the box.

Re: Mercruiser 470 3-wire alternator wiring question

Thank you for the replies. I took a second look at the choke wiring (one wire is black - and one is white +) as suggested. I followed the harness down and there was a purple wire looped around coming out of the harness and going back in... So, I unhooked the alternator wiring from the white choke wire and put it on the purple - now the engine shuts down when I turn the key as it should. It was charging at 14.7 (battery was a little low) when it was wired up to the choke wire; now it stays solid at 13.3. I turned every accessory I had on, lowered the throttle, raised it, turned everything off and it didn't budge from 13.3V. I'm hoping I'm good now - This alternator is brand new - my last alternator let me have only 12.4-12.7 on a good day...

Don - I did a google search and came up with an article that says some ignitions have an Acc position... Mine is just off, on, start.

Thanks again guys, for the fast responses!

Re: Mercruiser 470 3-wire alternator wiring question

Mine is just off, on, start.

Click to expand...

That is 3 positions. Off is a position. If it had acc., it would be a 4 position.

As far as the alternator goes, don't look at wire color only. You never know if someone replaced a wire with a different color or not. Look at where it goes.

My 2004 Bayliner 194 is having an issue. When I turn the key to turn it off it stays on? I heard that it could be the diode on the alternator gone bad. Someone suggested I can install and external idiode but I don’t know exactly how that would work. Does anyone have a simple diagram that I can follow.

Please don't post to old threads (read the forum rules). If you have a question, start a new thread of your own.

Thread closed.

Chris
iboats mod team.