Alternator hookup on Sunbird OMC

lakenormangal

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I have a 1990 Sunbird with a 4.3 OMC and I bought a new alternator. The new alternator is a little different and it's very unclear what goes to what. We know where the positive goes, but the other 3 leads are confusing. I'm not the mechanic but my brother and bf are working on it and they are confused about which leads go to the starter, the fuel pump, ect. Is there anyone here with an OMC that can help.
The new alternator has these different labels on the posts. The only one we know is pos. The others are R, I and remote sense. No idea what those are and which wires should go to those. Thanks.
 
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lakenormangal

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The thing is, the new alternator has 7 hookup posts on the back of it. The old one only had 4. And this next question is kind of a very simple question but is an excitation lead? Where does that hook up to? Thanks.
 
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lakenormangal

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Ok, this is,very confusing. The paperwork that,came with the alternator is,different from what is on the actual alternator. The paperwork says the names,of the posts are different than they actually are. I was wrong about that in my first post in this thread.

There are 6 posts on the back of the new alternator. They are labeled, L2, P, B, E, S and EXC.
 
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lakenormangal

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OK, I found some info, a wiring diagram from a Mando(?) which has the same post labels as the new alternator for the Sunbird. But one of the posts is for Remote Sense. And I found this ( below quote) that concerns the remote sense post. Does a jumper wire need to be connected?

"The "S" or sense wire or terminal is usually jumpered to the "B" terminal on the alternator to provide feedback of battery voltage to the regulator circuit inside the alternator. Sometimes, if a diode battery isolator is installed in the boat, the "S" connection may be connected to the battery side of the isolator to provide more accurate voltage feedback to the regulator to compensate for the drop through the isolator diodes. But that is not a very common situation."
 

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mjf55

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There needs to be a wire on the sense line. This is what tells the alternator to stop charging the battery ( it is part of the regulator circuit in the alternator). Some systems have it jumpered to the alternator output, but then it really is not checking the battery.
You need to have these 4 hooked up: Exciter ( EXC) , sense, output and ground.

Question: your wiring harness should already have the required wires and their destinations correct, You should not need extra wires. What doe the harness look like , what are the wire colors. We can make sure it is hooked up corrected
 
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lakenormangal

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Question: your wiring harness should already have the required wires and their destinations correct, You should not need extra wires. What doe the harness look like , what are the wire colors. We can make sure it is hooked up corrected

Here's what I got so far ( BTW, a 1990 Sunbird with an OMC Cobra) A prestolite came off the boat, but when the guys here got me a new alternator, they got a Mando style and they insist it will be the same once its hooked up.

Wire colors from the wiring harness for the alternator
(What wires I know)
Thick orange wire = power ( goes to the B terminal)
Black wire =ground (goes to the E terminal)

(What wires I don't know or am not sure of)
Gray wire = tach??? Cobra manual says the gray wire is tach. ( goes to the P or AC tap???)
Gray with white stripe = no clue, not listed in manual.
purple with red stripe wire = very confused, some say it goes to the S or sense terminal, other info says it goes to the EXC or exciter terminal. Cobra manual says the purple with red is the ignition resistor wire, but no idea which terminal it goes to.

Now I do have an manual for the Cobra and in the wiring color codes, the only wire it doesnt list is the gray with white. Could it be the trim gauge or trim switch? Or nav lights??

Thanks guys, I really want to get this back in the water and the experts at my house are not much help. So its up to me. Yikes!
 
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lakenormangal

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Ok the gray with white stripe wire is actually purple with white stripe. It faded.
I did not remove the alternator, and they guys who did, didn't label what wires came off what terminal. They took pictures that don't show everything.
Here's how the old one was hooked up best I can see from the pics.

orange wire to B terminal ( power)
Black wire ( ground) to EXC
purple with red stripe to EXC
purple with white stripe to AC TAP

That leave the gray wire and the sense terminal. I can see on the old alternator that something was hooked to sense. In the photos, you cannot see the sense terminal or the gray wire.
One would guess that the gray wire went to the sense terminal BUT I don't want to screw something up if I'm wrong.
 

mjf55

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If the black wire is really a ground, it should not go to the EXC terminal
If you need a service manual, go to the OBM I?O forum, Adults Only thread,; OMC information and you will see a link to the service manual
From that manual, page 135 ( 3-59) shows the alternator wiring.
  1. POS terminal is an ORANGE 10 Ga wire that goes to the assist solenoid
  2. AC terminal is a PURPLE/WHITE 16Ga wire goes to the choke
  3. S terminal is a PURPLE 16Ga wire that goes to a splice and continues to the Main Cable Connector
  4. EXC terminal is a RED/PURPLE 16 Ga wire that goes to the same splice as in above (#3)
    1. Note : S and EXC may be swapped, but since they go to the same splice, it does not matter
No Sense wire was used in the wiring harness. You Need to connect a new wire to either the POS terminal on the alternator or to the battery. We need this for the Mondo alternator.
 

lakenormangal

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On the alternator that came off of the boat there was a grey wire that was connected to the S terminal on the old alternator. So I'm hoping that this wire will also go to the S terminal on the Mando alternator.
Or do I need to run a wire to the POS terminal from the S terminal? This is where I'm getting confused.
There is no solid purple wire coming out of the wiring harness at the alternator point.
I will be connecting the ground wire to the Ground Terminal on this new alternator I don't know why they had it running to the EXC terminal.
 

bruceb58

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Ok the gray with white stripe wire is actually purple with white stripe. It faded.
I did not remove the alternator, and they guys who did, didn't label what wires came off what terminal. They took pictures that don't show everything.
Here's how the old one was hooked up best I can see from the pics.

orange wire to B terminal ( power)
Black wire ( ground) to EXC
purple with red stripe to EXC
purple with white stripe to AC TAP

That leave the gray wire and the sense terminal. I can see on the old alternator that something was hooked to sense. In the photos, you cannot see the sense terminal or the gray wire.
One would guess that the gray wire went to the sense terminal BUT I don't want to screw something up if I'm wrong.
Measure the voltage on this grey wire that you thought was hooked up to the sense. If it has full battery voltage on it then it can go to the sense. If it doesn't, make a jumper between the excite and the sense and don't use that grey wire.

You just can't leave the sense open. It has to somehow get battery voltage when the engine is running. Make sure that the excite wire has voltage with the ignition on and no voltage with ignition off.
 
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lakenormangal

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Measure the voltage on this grey wire that you thought was hooked up to the sense. If it has full battery voltage on it then it can go to the sense. If it doesn't, make a jumper between the excite and the sense and don't use that grey wire.

You just can't leave the sense open. It has to somehow get battery voltage when the engine is running. Make sure that the excite wire has voltage with the ignition on and no voltage with ignition off.


Thanks!! I will do these checks you suggested. I'm starting to understand this. Ok, silly question, but remember I work as a painter, not a mechanic, what would be full battery voltage, 12V?
In the wiring diagram in the OMC manual it shows the wire from the Sense terminal and the wire from the EXC joining together into one wire and going into the main cable connector.
And I found the correct part number for the old alternator in the OMC manual. And on a number of marine parts websites, this Mando is listed as a direct replacement for that model of Prestolite.
 

bruceb58

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Battery voltage for a fully charged battery is 12.7V with the engine not running and after being off any charge for around 20 minutes.

After all of this, you will know more than 95% of boaters how alternators are hooked up.
 
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lakenormangal

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Battery voltage for a fully charged battery is 12.7V with the engine not running and after being off any charge for around 20 minutes.

After all of this, you will know more than 95% of boaters how alternators are hooked up.

One other thing, the stock alternator does NOT have a ground wire! I found this out by looking at the OMC manual. Its grounded at the adjuster clamp. Now as this is NOT a Prestolite, do I need to run a ground wire to the E post on the Mando alternator? I was thinking of doing it anyway just to be on the safe side. I love my little boat and don't want anything to happen to it.

That black wire I was talking about? That goes to something else, its a wire the former owner ran that keeps the alternator from over charging ( same as sense?) or something very similar. I think he said it tell the alternator when to charge and when to stop. On the old alternator that wire ran to the EXC and with the purple/red wire. He's coming over tomorrow and hopefully with all this info, we can get the new one hooked up correctly.

The old alternator going bad is the only engine problem so far, the boat ran great for the 1 1/2 years he had it, and the 1 1/2 years that I've had it. It starts up at the first turn of the key, most of the time, and runs smooth as silk. In fact the only real problem is that I did not know how to properly shift it at first and I got it stuck in between gears the first time I had it out.
Oh yeah, and the time I hit a rock with the prop last year ( I'll keep plenty of room under that boat now! And ONLY aluminum props for me! Too many things in the water at Lake Norman.)

I try to know all I can, cos when it comes down to it, its my boat, and my guys might not always be there when something goes wrong. Thank goodness for this forum and folks like you who help out.
 

bruceb58

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It doesn't hurt to add the ground wire although I doubt it's really needed.
 

bruceb58

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Instead of posting on your other thread, I will ask my question here. You said it has an electric fuel pump but in 1990, no OMC's came with electric fuel pumps. Was it added later? Hopefully, whoever added it has it wired through a relay driven by an oil pressure switch.
 
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