mercruiser 3.0l alternator question

[kart74]

I have a 1983 mercruiser 3.0l serial number 4524932. The alternator doesn't seem to be doing anything. Battery voltage is the same with engine running or not and at any rpm. I looked in the service manual and from what I am seeing this isn't a stock alternator. There is the output wire, and then one other wire coming out of the back of it that is red. It wasn't hooked up to anything but had a male bullet connector on it. I also found a purple wire coming out of the harness y the alternator with a female bullet connector that wasn't plugged in. I checked and the purple wire has 12v to it. I tired connecting that to the red alternator wire, but made no difference. Any thoughts?

 

[alldodge]

Re: mercruiser 3.0l alternator question

I have a 1983 mercruiser 3.0l serial number 4524932. The alternator doesn't seem to be doing anything. Battery voltage is the same with engine running or not and at any rpm. I looked in the service manual and from what I am seeing this isn't a stock alternator. There is the output wire, and then one other wire coming out of the back of it that is red. It wasn't hooked up to anything but had a male bullet connector on it. I also found a purple wire coming out of the harness y the alternator with a female bullet connector that wasn't plugged in. I checked and the purple wire has 12v to it. I tired connecting that to the red alternator wire, but made no difference. Any thoughts?

Take a pic of what you have and post so we can have a look.

The wiring should be about what I have posted below. There is an Orange wire going to the starter which is connected to the battery. The Org wire could have been replaced with Red. The purple wire is for the field windings and becomes hot (12V) when the key is turned to ON. There also use to be a Red/Pur, but most the time there are 2 other wires which connect to the field windings on the Alt with banana jacks

 

[kart74]

Re: mercruiser 3.0l alternator question

here are the pictures. Thee is the orange output wire that goes to the starter and then there is a red\purple wire coming out of the back of the alternator. On the wire harness side I have a open purple wire and I have an open large gauge red wire that looks to go to the starter solenoid.

 

[alldodge]

Re: mercruiser 3.0l alternator question

Looks like a conversion has taken place. The black plug looking think with the red wire coming out of it is an adapter. Don't know if you have a aftermarket auto or marine alternator there. If it is a marine alternator I would take it to autozone or the like and have them test it. If it's not a marine alt then I would go get another before an explosion happens.

Pull the alt and see what kind of numbers you can find on it. A marine alt will have screens over every opening.

The Purple wire use to go to the alt when two wires were used. If the Red wire stays hot all the time then it may have been replaced and may be the other lead to the alt, don't know would need to dig more. Need to find where it comes out on the other end.

 

[kart74]

Re: mercruiser 3.0l alternator question

OK so I just took it off. the red wire I was talking about is actually red\purple as well. It is a marine alternator as it has screens and is stamped marine. I cant find a manufacturer but it has 2 numbers stamped on the top. It says 1105064 42A 83A10 12V NEG. The adaptor looking plug is actually part of the alt. It cant be pulled out or anything. There is a hole in it where it looks like there may have been another wire coming out at one time. Maybe that's the issue. I am going to take it to a auto store and have it tested. THanks.

 

[alldodge]

Re: mercruiser 3.0l alternator question

OK so I just took it off. the red wire I was talking about is actually red\purple as well. It is a marine alternator as it has screens and is stamped marine. I cant find a manufacturer but it has 2 numbers stamped on the top. It says 1105064 42A 83A10 12V NEG. The adaptor looking plug is actually part of the alt. It cant be pulled out or anything. There is a hole in it where it looks like there may have been another wire coming out at one time. Maybe that's the issue. I am going to take it to a auto store and have it tested. THanks.

Sounds good, Your Red/Pur wire should be there, the other wire should be the Purple. Without the Pur connected the alt won't work

 

[tinkerguy70]

Re: mercruiser 3.0l alternator question

The plug in the back that won't pull out is actually made into the screen cover. It's part of the explosion proofing. If you remove the screws holding the screens on (the case bolts) you will see that it actually plugs into the original 2 wire GM plug. Your missing wire is probably behind that plug.

Like AllDodge said, take it and get it checked. If it checks out OK, and you get all your wires fixed, but then find that it's still not charging, check the white fuse mounted on the starter that the Orange wire goes to.

Good luck!

 

[airshot]

Re: mercruiser 3.0l alternator question

Just a note here, do not waste you time going to autozone or other auto suppliers as they do not have the knowledge to test marine equipment. You might have an exception if you live in a boating town but in general they will not touch marine equipment, I found out the hard way. If you have a reputable starter/alternator rebuilder in your area have them check it out and they will also help you with your wiring. I had a similar situation a few years back and found a local rebuilder and he solved all my problems and his advice and knowledge was well worth the few bucks he charged.

 

[tinkerguy70]

Re: mercruiser 3.0l alternator question

^^^^ What he said. I meant to tell you that previously. Good catch airshot!
If the big box part stores don't have an automotive application to plug into their tester, they will be lost. You might have some luck at NAPA, but it's doubtful.

If I where you, and there wasn't anyone close to check it, I'd try to fix the wires and then try it out. It's an easy enough fix, likely worth your time.

 

[kart74]

OK so I took the alternator apart and replaced the purple wire that was missing. Got it all hooked back up and it works! 14.78v at the battery at all rpm. BUT then I went to shut it off and it wouldn't. Engine just keeps running with the key shut off. Disconnected the purple wire and engine shuts off. Tested the purple wire on the harness side and it has 12v with ignition on and 0 when off. I am guessing this means the alternator is actually bad. Am I correct?

 

[Bt Doctur]

Either you have those 2 wires reversed or a diode in the alt is bad allowing it to backfeed power