Alternator wiring

"I've got a merc 165 l6.

"I've got a merc 165 l6. I can't seem to get my alternator to charge my battery. I took the alternator to get checked and it's working, so it must be the wiring. The only reason I'm on here for wiring advice is because it's Saturday and I'm with an electrician who can help me, but I left my manual with the wiring diagram at home. So, I'v got two wires going to the alternator. With a voltage reader I'm getting 11.8 volts at the alternator and 12 volts at the battery and that's with the boat running. Is there supposed to be more wires running to the alternator. Any advice helpful. I realize its Saturday and you're all probably out on your boats right now. but maybe someone out there is at home doing the same thing I'm doing. thanks"

"Should be four wires going to

"Should be four wires going to the alternator orange,purple,red/purple, and black and if you have an electric choke then you will also have a purple/yellow.. hope this helps and not to late for you.. good luck"

"What year is the boat? What

"What year is the boat? What color are the wires to the alternator? How many wires are connected to the alternator?

A four wire alternator has a black ground wire, orange output wire, purple sensor wire and a red with purple stripe excitation wire. These last two wires tell the alternator what the battery voltage is and when to start charging the battery.

The orange 10 gauge output wire can corrode and reduce the current getting to the battery. The maximum output of the alt. when needed is 14.8 VDC. If your battery is going out it could fail to accept a charge from the alternator. Have it load tested."

"My boat is a 1976 Somerset 16

"My boat is a 1976 Somerset 165. The battery is bran spankin new and it reads 12 volts so it can't be that. I got my seloc manual now and it shows just two wires running to the alternator and that's what i've got. A red wire with white stripe and a black ground wire. My dad, who is an electrician, and I went through all the wiring today and we can't find anything wrong with it. All the wires are where they should be and everything rings out good. I'm stumped. The alternator checked out good, the wiring checked out good, and the battery checked out good. Any thoughts?"

"might be a bad wire or even w

"might be a bad wire or even wrong alternator pulley run two new temp wires and see if that makes a difference also make sure both the ground on the battery and the alternator are good and clean (pull all the connections and sand them down) other then that you have me stumped also, if you figure it out please reply back.."

another thing check your belt

another thing check your belt make sure the tension is good and tight and also make sure even if it is tight that it is not slipping in any way..

"Graham:

"battery is

"Graham:

"battery is bran spankin new" only means new to you. It may have sat on the shelf for a year which is not good for it. I would look for the date code on it to determine when it was made. I have had a "NEW" battery fail in one week.

I am looking at the wiring diagram for your engine. The alt. output wire (red-white) runs thru the main engine plug, pin #4, and comes back thru pin #6, red wire and goes to the 40 amp CIRCUIT BREAKER(CB). The output of the CB, red wire, goes to the SLAVE START solenoid, connects at it and bypasses it on its way to the STARTER where it meets with the main battery cable.

Parts to check; voltage checks with a Digital Volt Meter (DVM):

1 - main engine plug; check for corrosion on pins 4 & 6 (and any others while you are looking)

2 - 40 AMP CB: (on the engine) due to its age the contacts inside may be corroded and may be providing a resistance to the charge voltage. Measure the voltage on both terminals; voltage should be exactly the same. If voltage is different, clean the wire terminals and recheck the voltage; change the CB if there is ANY drop in voltage at all.

3 - SLAVE SOLENOID: Remove and clean the two RED wire terminals and reattach.

4 - STARTER: Remove and clean the two RED wire terminals and reattach.

Old wiring harnesses on boats, especially the engine harness, tend to corrode internally. The copper wire strands wick moisture into the insulation and turn the copper strands dark brown or crud blue. Since current travels on the outside of the individual strands of copper, it is important that they remain clean like a new penney.

I have had some success replacing the terminal connectors on a number of wires. After removing the terminal I strip back an inch or two if enough wire is available to find shiney wire. If I don't find it, I use a small piece of medium grit sand paper and wrap it around the bare wire strands and pull the wire thru the sand paper until it is shiney. Then I twist the wire and tin it, first dipping it in flux, using rosin core solder. I then crimp it to the new terminal and solder the wire to the terminal. Note: I like to use terminals with SHRINK TUBING all ready attached to make a water tight seal.

You might have to change all of the terminals for the alternator to operate at peak efficiency.
But I suspect the 40 AMP BREAKER is the culprit if not part of the problem along with "past its prime" wiring harneses.

I changed all the wiring in my 87 Baretta last year due to GREMLINS like your problem and they have not come back. Fingers crossed. Good luck."

guy not to butt in but shouldn

guy not to butt in but shouldn't he be getting higher voltage at the alternator regardless of the wires that you are referring to. he says he is only getting 11.8 at the alternator with the engine running. generally the output at the alternator should be around 14 or so right..

"Thanks for responding Bill an

"Thanks for responding Bill and Guy. The alternator belt is good and tight and the alternator is spinning as it should. I made sure to check that on Saturday. And Guy, I'm getting 12 volts at the battery so doesn't that mean it's ok? I'm not sure how else to know if a battery is failing. And I was having the same problem with my old battery so I'm pretty certain it's not that.

As far as the alternator goes, I guess there's a chance the guy at the alternator shop could be wrong, but, they usually tell you it's no good and want to sell you a new one, so the fact that he said it was good makes me want to believe him. And it was not at Autozone or Advance auto parts or one of those shotty places, it was at a dedicated radiator and alternator shop, so he knows what he's doing.

Back to the wiring, let me make sure I'm getting this right. You want me to bypass the starter solenoid and put a jumper on to the starter positive lug? Or should I go from the starter soleniod straight to the positive battery lug, and bypass the starter soleniod and the starter?

I'll go through this weekend and clean and check all the connections and try bypassing some things and see what happens. Also, does it matter which screw on the alternator the ground wire goes to. I know I've got the hot wire on the right lug, but there's two different screw the ground could go on. The screw that the ground wire is not on has a bracket that's ties the voltage regulator to the alternator, and I'm not sure if it's just for support or for grounding purposes.

One other thing I just thought of, Shouldn't I be getting 14 volts or higher at the alternator with it running. I was getting less voltage at the alternator when it was running. Just because the wiring might be bad doesn't mean I wouldn't be getting 14 volts right at the alternator. So....... doesn't that mean the alternator IS bad?"

"((One other thing I j

"((One other thing I just thought of, Shouldn't I be getting 14 volts or higher at the alternator with it running. I was getting less voltage at the alternator when it was running. Just because the wiring might be bad doesn't mean I wouldn't be getting 14 volts right at the alternator. So....... doesn't that mean the alternator IS bad?))

this is why I think it has to do with the alternator and not the wiring if the alternator is bad or the wrong one it will do the same and not charge.. take it to another place (I know you don't like autozone) but you can watch them test it and get a print out of the results also you can have them pull a new one from stock and make sure that it is the same (all marine parts have a like automotive part) it's the internals that are different.. or if the alternator is old it's probably a good thing to just go ahead and replace it and then you know for sure it's not that.."

"Graham & Bill:

Jump

"Graham & Bill:

Jump in anytime Bill.

I took the statement as having been tested as it being OK but had some doubt. When you are tired, you miss important points. Thanks for catching it.

Graham: I was just stating the voltage travel in the alternator ciruit and stated the wire circuit "bypasses" the solenoid, meaning it only uses one side of the solenoid as a terminal point to "drop off" voltage there and the wire continues on to another point. DON'T BYPASS anything. Read it again as you look at the wire schematic.

In most cases, the ground wire will attach to a stud on the alt. case. Cars use the case connection to the engine as the ground on a single wire alt. which is basically what you have. Check the wire connections you made to the alternator. Your ground may be in the wrong place which may also have cooked the alt. Sorry for the confusion.

Did the alt. shop "load test" it? Maybe he damaged it during testing and that's why you have low output. Take it back to him to restest it."

"I think I'll definetely h

"I think I'll definetely have the alternator checked again. By the way, I did take it to Autozone and Advance Auto Parts before I went to the specialist and both of those places told me they can't test marine alternators. I couldn't figure that one out. I don't see why they can't test them. They probably just didn't feel like doing it, which doesn't suprise me. The employees there usually don't give a @*$%.

But thanks for all the knowledge and advice. I'll try and let you know what happens."

After reading these posts I fe

After reading these posts I felt like I was reliving the last three months of my life!! Was only getting 12.8V at the battery and 12.9V at the alt. Put a new alt in and now get 14.7 everywhere and have had no problems!! Bought the reman alt from this site and life is now good! Good luck

I don't know if the 165 me

I don't know if the 165 merc has the same wiring as my 260 merc. But I just fixed this problem this weekend and found that the new starter I had installed 3 weeks ago was not wired properly. The orange wire that come off the alternator should be connected to the same terminal as the battery is on the starter. I had 12.6 volts at the battery and 11.4 volts at the alternator when it was running. When I place the orange wire coming from the alternator on the battery terminal of the starter all was well. I traced the orange wire and it whent straight to the starter so you might have a bad wire there.

I forgot to some more info. My

I forgot to some more info. My alternator is brand new and I noticed this problem only after I changed it. So I went and had it checked at NAPA where I bought it and they were glad to check it. It was fine that is when I broke out the wiring diagram and started tracing wires.

"Michael, thanks for the repy

"Michael, thanks for the repy.
I went through all the wiring last weekend and found nothing wrong. The wire coming from the alternator is on the same lug as the wire coming from the battery. My question to you is. Shouldn't you still have 14 volts at the alternator with it running? Just because your wiring was bad doesn't mean your alternator wouldn't still be putting out 14 volts. It just wouldn't be supplying your battery with 14 volts.
I went ahead and bought a new alternator off this site yesterday, so we'll see if that fixes my problem. I'm almost positive my wiring is good.
I didn't know that napa sold marine alternators. I hope you didn't buy a regular automotive alternator? There is a difference."

"I'm sure it was a marine

"I'm sure it was a marine alternator. I thought the same thing. Reguardless it should put out 14 plus volts, but it didn't. I spoke to a mechanic and he told me that it had something to do with the load put on the alternator. Everything is fine now and everything is charging."

"Hey, thanks for the input. I

"Hey, thanks for the input. I hope my new alternator makes my problem go away too.
It's good to hear other success stories. Happy boating!"