75hp Mariner not charging battery anymore

quackerkiller · May 19, 2010

I have an '88 (maybe '89) 75hp 3 cyl that has quit charging my cranking battery. Charging before I go out is a pain and unsafe (don't wanna get stranded!) How do I diagnose what needs to be replaced? It looks like rectifier and stator issues are pretty common? I feel comfortable replacing parts but I feel lost on the diagnosis. I appreciate any help folks. Please and thanks in advance!

Edit: Tach doesn't work anymore either. I don't really care about that but if it is part of the problem, I figured I should mention it.

ajgraz · May 19, 2010

Re: 75hp Mariner not charging battery anymore

Check rectifier first using an ohmmeter, preferably with a diode/continuity function:

Yellow wire 1:
Red lead: red wire; black lead: yellow wire = no continuity (or "high" resistance)
Red lead: yellow wire; black lead: red wire = continuity (or "low" resistance)
Red lead: yellow wire; black lead: case ground = no continuity ("high")
Red lead: case ground; black lead: yellow wire = continuity ("low")

Then repeat these tests with yellow wire 2.

(All these tests to be done with rectifier installed and all wires attached to motor. "Lead" means the lead from the meter))

If you pass all these tests, rectifier is good. If you fail any of them, rectifier is bad.

quackerkiller · May 19, 2010

Re: 75hp Mariner not charging battery anymore

Thank you for the quick repsonse and my first task! I am heading to pick up a multimeter and conduct the test. Who wants to assign my next task?! Thanks again.

quackerkiller · May 19, 2010

Re: 75hp Mariner not charging battery anymore

Alright, I just went to check the rect (3 node) and found that it has two yellow wires, a gray, and a red. The Red wire is coming from the top node, a yellow from each of the other two nodes, and a gray coming from the rear node (which has a yellow)

sschefer · May 19, 2010

Re: 75hp Mariner not charging battery anymore

The two yellow wires are comming from your stator and are a/c input. The red wire is the output (charges your battery) the gray is your tach.

Use a simple 12v probe style tester that you can get at any autoparts store. They usually have a neon light in the handle.

Disconnect the battery. Do not disconnect any of the wires to the rectifier/regulator.

Connect the black wire to a suitable ground point on the engine block and put the probe tip on the red wire. Start the engine and the light should glow bright.

Remove the probe tip from the red wire and put it on either of the yellow wires. The bulb should be dim but if you accellerate the engine it shoud brighten. Test both yellows.

If the light comes on at the red the rectifer is ok and the stator is o.k. replace the battery or replace or clean the battery cables and connections.

If the light does not come on at the red but does at both yellows then replace the rectifer/regulator.

If the light does not come on and brighten with increased RPM at one or both yellows replace the stator.

I doubt its the battery or cable because the tach quit.

quackerkiller · May 19, 2010

Re: 75hp Mariner not charging battery anymore

Ok, I just tested using ajgraz's method and just used both yellows and assumed the gray was "black". The rectifier looks good according to my tests. I will check now using sschefer's method. I will just check the voltage using the multimeter instead of the neon lights, should be the same thing right... Thanks so much for the help guys. I have a trip this weekend and am in cruch time now. If I knew you were from around here, beers would be on me!

ajgraz · May 19, 2010

Re: 75hp Mariner not charging battery anymore

quackerkiller said:
Ok, I just tested using ajgraz's method and just used both yellows and assumed the gray was "black". The rectifier looks good according to my tests. I will check now using sschefer's method. I will just check the voltage using the multimeter instead of the neon lights, should be the same thing right... Thanks so much for the help guys. I have a trip this weekend and am in cruch time now. If I knew you were from around here, beers would be on me!

Nah, gray wire will play no part in checking the diodes in the rectifier.

Maybe I wasn't clear...

"Red lead: red wire; black lead: yellow wire = no continuity (or "high" resistance)"

Means "red lead from meter touching red wire rectifier post and black lead from meter touching yellow wire rectifier post should show no continuity."

And so on.

And "case ground" means the bare metal case of the rectfier, since it grounds through that. If the rectifier is installed, you can use any ground on the powerhead instead.

quackerkiller · May 19, 2010

Re: 75hp Mariner not charging battery anymore

schefer, if I disconnect the battery, how am I supposed to start this thing? Don't tell me I have to pull start this hog...

quackerkiller · May 19, 2010

Re: 75hp Mariner not charging battery anymore

aj, the gray was coming from the same post as one of the yellows, so results are the same. I misread initially and was looking for a black wire but I see what you meant.

I just tested according to schefer (minus disconnecting the battery). I just left it connected and started the motor, ran the tests. Both the red and the yellow had a voltage while idle (40% on red and 20% on front yellow and 0% on the rear yellow using a 12V battery tester) The 20% front yellow did increase to 30% with a little more rpm. Schefer, does this mean bad stator or battery. You state that if it comes on at red, stator and rect are good, replace battery (It does come on at red). You also state that if one or both yellows dont come one, replace stator (which is the case also). I assume the stator needs replacing?...

Thanks again guys!

ajgraz · May 20, 2010

Re: 75hp Mariner not charging battery anymore

quackerkiller said:
aj, the gray was coming from the same post as one of the yellows, so results are the same. I misread initially and was looking for a black wire but I see what you meant.

I just tested according to schefer (minus disconnecting the battery). I just left it connected and started the motor, ran the tests. Both the red and the yellow had a voltage while idle (40% on red and 20% on front yellow and 0% on the rear yellow using a 12V battery tester) The 20% front yellow did increase to 30% with a little more rpm. Schefer, does this mean bad stator or battery. You state that if it comes on at red, stator and rect are good, replace battery (It does come on at red). You also state that if one or both yellows dont come one, replace stator (which is the case also). I assume the stator needs replacing?...

Thanks again guys!

What are these percentages?

If the diode check on the rectifier was OK, and you are sure your battery can take a charge (you said you've been charging in the garage?) then it sounds like a stator issue to me, likely one or both of the yellow charge wires are corroded away. It may be possible to repair those, depending how bad the corrosion is and how far up the wire.

Have you had any issues with how the motor runs? Especially at rpm >2500 or so? Wondering if there might be any problems with the windings in the stator, which would show as not only poor charging, but weak spark.

CDI Tech Support · May 20, 2010

Re: 75hp Mariner not charging battery anymore

quackerkiller said:
I have an '88 (maybe '89) 75hp 3 cyl that has quit charging my cranking battery. Charging before I go out is a pain and unsafe (don't wanna get stranded!) How do I diagnose what needs to be replaced? It looks like rectifier and stator issues are pretty common? I feel comfortable replacing parts but I feel lost on the diagnosis. I appreciate any help folks. Please and thanks in advance!

Edit: Tach doesn't work anymore either. I don't really care about that but if it is part of the problem, I figured I should mention it.

Whenever there's a charging issue & the tach doesn't work, it could be a stator or regulator/rectifier failure.

More often than not, regulator/rectifier & stator (battery charge windings) failures are attributed to improper battery type and/or battery charging neglect.

Thoroughly read our article on Batteries & Regulator/Rectifiers before taking the next step:

Battery Charging Issues, Regulator-Rectifiers and Tachometers

CDI Tech Support · May 20, 2010

Re: 75hp Mariner not charging battery anymore

quackerkiller said:
Alright, I just went to check the rect (3 node) and found that it has two yellow wires, a gray, and a red. The Red wire is coming from the top node, a yellow from each of the other two nodes, and a gray coming from the rear node (which has a yellow)

What you have a 3-post rectifier. No regulator involved.

Even though it's connected to the rectifier, the tach gets its feed via the stator.

Anytime you have a charging issue involving a 3-post rectifier, we suggest upgrading to a combination regulator/rectifier. With only a rectifier, the battery is having to act as its own regulator. A combination regulator/rectifier takes that strain off the battery.

More than likely, the battery is in need of replacement since there is a charging issue. Upgrading to a combination regulator/rectifier + a new proper style battery (see our Battery guide in my signature to determine proper style battery) will give your battery, regulator/rectifier & stator optimum life, as long as you trickle-charge (via a battery charger) the battery overnight before each & every use of the boat.

We suggest part# 194-5279 List price is $158.00. We sell direct or you can purchase through iboats.

CDI Tech Support · May 20, 2010

Re: 75hp Mariner not charging battery anymore

ajgraz said:
Have you had any issues with how the motor runs? Especially at rpm >2500 or so? Wondering if there might be any problems with the windings in the stator, which would show as not only poor charging, but weak spark.

A stator on an ADI (alternator-driven ignition) is a 2-part apparatus...battery charge windings that encompass 3/4 of the stator (yellow wires) & charge coils (typically red & blue wires on a Mercury stator).

If the battery charge windings on the stator are faulty, but the rectifier is good, this would not cause spark issues.

However, a rectifier failure definitely can cause anything from a No Spark condition to a high-speed miss. The reason why is because if a diode is shorted inside the rectifier, that creates a 2-way path, thus 12VDC from the battery can then flow to the stator's AC magnetic field, creating havoc in charging the stator's charge coils, which supply voltage to the switch box.

quackerkiller · May 20, 2010

Re: 75hp Mariner not charging battery anymore

The percentages are read off of my battery tester (I'm assuming they are voltages).

The battery does take a charge. After it died last weekend, I charged it up and used it again on Sunday morning.

It runs pretty good other than this issue. It bogged down once last summer at higher rpms but it ran fine after that issue. Im not sure what that was but it has been running great since.

I thought I remember reading something about if you cross the battery terminals and hook it up backwards it can cause one part or the other to fail. Could that be a possibility? I don't recall doing so but I can't guarentee anyone else hasn't.

CDI Tech Support · May 20, 2010

Re: 75hp Mariner not charging battery anymore

quackerkiller said:
The battery does take a charge. After it died last weekend, I charged it up and used it again on Sunday morning.

If your battery is dying after one boat use, it's time to replace the battery. If all the battery is being used for is to crank the engine, a well-charged battery should crank the engine several times before dying.

If your battery does this, is more than one year old, is a closed-case battery, a supermarket or automotive store battery or a deep cycle battery, it's time to purchase a proper style battery.

And if it meets one or more of the above criteria, that's more than likely the reason why your stator and/or rectifier has failed.

See this guide for the proper style battery:

Battery Charging Issues, Regulator-Rectifiers and Tachometers

quackerkiller · May 20, 2010

Re: 75hp Mariner not charging battery anymore

It is starting the battery on and off all day (10-30 times), running wide open, trolling, radio, lights etc. It runs all day pretty well considering it isn't being charged (or I suspect it isn't). I'll have to check what kind of battery it is though and get back to you tonight.

If the diode tests checked out and the rect passed the tests as mentioned above, can I rule that piece out? If I am to just put in a new stator and if that does't fix it, put in a new rect, do I run the risk of ruining the new stator if the rect is bad?

sschefer · May 20, 2010

Re: 75hp Mariner not charging battery anymore

quackerkiller said:
schefer, if I disconnect the battery, how am I supposed to start this thing? Don't tell me I have to pull start this hog...

I was referring to the red on the regulator/rectifier not the battery cable. If the red is connected to battery then you're light will light from the battery voltage and you'll get a false reading. I should have been more clear. Just check red for charging voltage with the multi meter.. You'll probably see around 13.5V if everyhing is good. When you put the meter on the yellow don't forget to switch to A/C.

Does that help?

ajgraz · May 20, 2010

Re: 75hp Mariner not charging battery anymore

If the rectifier passed the diode tests, it is OK, you can rule it out.

There are tests you can run on the stator using the ohmmeter; but they do have limitations:
1) They do not necessarily tell you about charging circuit, but rather the low and high speed windings
2) They are not definitive; if the stator fails these tests, it is bad...but it can pass these tests and still be bad.

Stator leads disconnected from switchbox
Low speed windings: Test between blue wire and red wire; should be 5400-6200 ohm
High speed windings: Test between red wire and powerhead ground; should be 125-175 ohm

So, if stator fails one of these tests, replace it. But even if it passes, the definitive test would be to get a DVA adapter for your ohmmeter, and test actual voltages produced by the stator while running the motor.

While you are looking at the stator, take a good look at the yellow wires; I still suspect your issue is corroded charge circuit wires off the stator, this is very common with these old Merc stators. That would explain no charge, no tach, yet no significant running problems.

quackerkiller · May 20, 2010

Re: 75hp Mariner not charging battery anymore

I will be doing these final tests tonight. Apparently the rect is fine. I will also check for corroded wires. If I find nothing else, I am jumping off the stator cliff. That, or the wires has to be the issue. The rect is apparently fine, the battery holds a pretty good charge, must be the stator. Thanks again guys. I will be spending another night in the garage, got tomorrow off to do the repair. Hopefully someone local has the parts otherwise I'll order and fix it next week. Maybe I'll bring another battery in the boat as a back up..that or a sail.

CDI Tech Support · May 20, 2010

Re: 75hp Mariner not charging battery anymore

ajgraz said:
Stator leads disconnected from switchbox
Low speed windings: Test between blue wire and red wire; should be 5400-6200 ohm

You mean Blue to Ground. The Blue (low-speed coil) is completely independent from the Red (high-speed coil)

ajgraz said:
So, if stator fails one of these tests, replace it.

Do not ever replace a component because it's only slightly out of resistance spec. Resistance is highly unreliable unless it's shorted or open. DVA is the only reliable measurement concerning an outboard.

Furthermore, quackerkiller has not mentioned experiencing a running issue, thus no checks to the low-speed or high-speed coils are necessary.

The proper DVA checks for a charging issue would be to measure DVA from the stator's Yellow to Yellow at idle. Should be 17-25V DVA connected to the rectifier & 17-50V DVA disconnected from the rectifier. This is mentioned in our "Battery Charging Issues" guide.

75hp Mariner not charging battery anymore

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