So I put on my shiny new alternator, fired up the Bukh all worked perfect.
I went to the boat yesterday to fix a little oil leak I had from the lift pump,
I started the engine, noting that the amp light came on with the ignition
and went out about 2 seconds after the engine started- perfect. However
when I had finished poking around the lift pump to check the leak I noticed
the amp light gently flickering on and off, an increase in revs made no difference.
So I assume it's because the battery is full and won't accept any more charge.
I have a small solar panel on the battery so it's always fully charged. Should the
amp light flicker like this or is something amiss.???

Sam bucka
See what size globe you have in the warning light it should not be more than 2 watts
Google it also to check the wattage
From my old brain its telling 2 watts no more
If it is the alternator will not charge

I really would not suspect the warning light HG, nothing has been touched there. The light goes out and stays out
after the engine has started and seems only to do this on/off thing after a while. The light is not bright like it is
when the ignition is turned on. There are three connections on the back of the alternator - one is a live lead from the
battery - one is a spade for the light - and one is earth. I was told that the alternator could earth through the bracket
it is attached to but when I tried that it didn't work so I had to run an earth wire to make it fire up. It seemed to work
perfectly when I first tried it but maybe i didn't look hard enough.

Sam sounds to me you may have a crook earth perhaps the resistance rises after a while of operation ...may be worth checking.

Hi Mad. Yes that's a possibility. I will see if I can move the earth wire down to the battery earthing point.
If you can't think of an obvious reason for this to happen then it has to be something like a crook earth
although I thought I had done a good job at the time.

Did you re check the belt tension? It may have slackened off after the initial running.

Alternators are weird. Some of them depend on the alternator light to actually charge, if your alternator light globe is blown then everything stops. There's always current going through the bulb, for whatever reason, which might be what you're seeing.

I would disconnect the solar panel, get out the multimeter, check the battery voltage before starting, after starting and then after running for 10 minutes.

Before starting I'd expect 12.6,
After starting I'd expect 13.2 or so,
After running for 10 minutes I'd expect 13.8.


If those voltages are close then you've got nothing wrong with your system.


Edit: Another thing you can do is try turning a high load on, like a light or pump, while the alternator light is doing its flashy thing.
What I think is happening is that you have such a low load on your system, that the regulator is telling the alternator not to generate much power at all, which means that it's low enough to make the light flicker. If this is the case then everything is working perfectly.

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Yes Shotchas. The belt is the first thing you see when you take the front off the engine casing,
plus it makes a squealing sound if it gets a bit too slack. So it's not that. But thanks for the input.

OK Nebbian got that. Yes I think my light needs to go out for the alternator to charge. I can do
what you suggest, sounds good to me. Thanks for comparative voltages, that's a big help.

Nebbian. Re edit. I think you've hit the nail. there was no load at all when this was happening. I have no 'electronics"
anything electric I have to turn on myself. I have an electric head and water to the galley but nothing that
requires a constant supply so usually everything is off even though I'm on board. Does that make sense???.

The alternator light is required to flash the fields. Each alternator requires a certain resistance with the bulb to excite the fields. You have changed to a different alternator and now you have to find what the new one needs to operate. Manufacturers site should have the details.

What voltage is the solar panel trying to put into the battery?
The alternator regulator may be sensing the solar voltage and throtelling back the output from the alternator ???

Select to expand quote

Ramona said..
The alternator light is required to flash the fields. Each alternator requires a certain resistance with the bulb to excite the fields. You have changed to a different alternator and now you have to find what the new one needs to operate. Manufacturers site should have the details.

spot on Ramona the warning light excites the field windings so it will charge . There are some alternator that don't need to do this mine is one of them
below is a quote off a holden forum


I recently upgraded to a VN V8 alternator in my HG. For anyone that is about to do it the plug is the same as an injector plug from a commodore and finding a 2w BA9s globe was a pain as the major places i went to autobarn, supercheap and repco didn't stock it and could only get me a box. I even tried an auto electrician.
For anyone one on the southside of Brisbane I found Cheapa auto spares at Oxenford have them on the shelf.




as you can see the warning lamp must not be any larger than 2 watts . a nice blue seas LED does the trick

I am not flash with electrics but when mine did this it was a failed diode due to my flashing the alternator up (started the donk) with no load on the alternator.
I suspect you have a blown alternator diode.

Select to expand quote

samsturdy said..


So I put on my shiny new alternator, fired up the Bukh all worked perfect.
I went to the boat yesterday to fix a little oil leak I had from the lift pump,
I started the engine, noting that the amp light came on with the ignition
and went out about 2 seconds after the engine started- perfect. However
when I had finished poking around the lift pump to check the leak I noticed
the amp light gently flickering on and off, an increase in revs made no difference.
So I assume it's because the battery is full and won't accept any more charge.
I have a small solar panel on the battery so it's always fully charged. Should the
amp light flicker like this or is something amiss.???

What was the charging (alternator) problem, in the beginning SAM?
On my wiring I ran the alternator charge wire B+ to my stater motor solenoid it in turns goes direct to the battery. are all these terminals ion good shape.
Usally when the lamp flickers as some one else has said already tend to be a diode.
But before you go down this path make sure your warning light is under 2 watts

Back to basics. Did you check the connections at all points that go to the alternator? I don't just mean the spade or ring terminals for being clean, I mean where the wire goes into the terminal itself. Before worrying about diodes or lights, check your terminals. Re-crimp them all, because a dry terminal when the alternator gets warm from operation will do exactly I what you're describing.

Select to expand quote

MichaelR said..
Back to basics. Did you check the connections at all points that go to the alternator? I don't just mean the spade or ring terminals for being clean, I mean where the wire goes into the terminal itself. Before worrying about diodes or lights, check your terminals. Re-crimp them all, because a dry terminal when the alternator gets warm from operation will do exactly I what you're describing.

I agree.

Try giving the alternator a tap with a hammer whilst its running, if one of the brushes is stuck and not making good contact, this usually frees it.

OK all, so much info. The original problem was a very noisy hot running alternator, the light wouldn't go out
until I revved to about 3000 revs, it would stay out. The replacement is the exact same alternator so all I
to do was bolt it on. There is little or no load on the alternator for most of the time, all it has to do is keep
a 100 AH battery charged to run the loo and pump water to the galley. There's also an auto pilot involved
when I get it working. So it seems to me that the problem lies with the alternator trying to charge a
battery that doesn't want charging and I tend to agree with nebbian's assessment, The thing must be
charging or the light would come and stay on, but it doesn't. I can see that the solar panel may be having
an influence so I'll disconnect it when I start the engine. And I will put a load on the system to see if the
light stays off. As HG says, 'there's always something'.

My experience is that the light won't necessarily come on bright and stay on if the alternator isn't charging. Flickering light means it isn't charging. Put a multimeter on your battery and check it with the engine running, it should read over 13v.
The state of charge of the battery is also not a factor, the light indicates the alternator is putting out a charge not the relative charge between the alternator and battery.
I had these exact symptoms a couple of years ago and am pretty confident you have a blown diode. From memory there are 3 diodes and with one out she won't charge properly.
If you just bought it it might be a warranty claim. I had to get mine fixed and it was about $50.

OK MB got that. Is there a test I can do to determine that a diode has blown?. For instance if I put a load on the battery
while its charging and the light goes off and stays off wouldn't that indicate that the system is working correctly and
therefore all the diodes are OK ???.

Firstly put the multimeter on the battery. If you are getting over 13v I am wrong.
If it is less than 13v I reckon it is time for an electrician to check it. Cheaper to remove it and take it to an auto electrician.

Select to expand quote

samsturdy said..


OK MB got that. Is there a test I can do to determine that a diode has blown?. For instance if I put a load on the battery
while its charging and the light goes off and stays off wouldn't that indicate that the system is working correctly and
therefore all the diodes are OK ???.

If you've got a blown diode then you'll get more than~ 0.5 V in AC mode when you put your multimeter on the battery.

But first things first, check in DC mode with engine off, engine started and after 5 minutes. That will tell us a lot about the health of the system.

Sam, you don't say whether you checked theconnections yet. The reason I mentioned it, was because I replaced an alternator, because the light was flickering, and then an electric fuel pump, because after replacing the alternator it wouldnt start. Then I replaced the starter, because it burned out trying to start the engine so many times when things werent correct. What I found, completely by mistake, was that the wire from the alternator to the starter, which was also the main battery feed, had broken inside the terminat that was securely attached to the alternator.

Had I checked the wiring, I woulholy have had to replace the starter, eventually. The upside is, I have a spare starter and alternator now.......

Yes, this is on an old Kombi, but it is exactly the same principle.

OK I've got all that. I did check wires and connections, but not too thoroughly nothing obviously wrong there.
I think checking the voltages is probably the way I want to go. It seems a positive way to determine wether the system is
doing what it's supposed to - or not. I have a multimeter so I can do that. I'll report back but I'm not going to the boat
until the weather has improved. The rain makes me go rusty.

Hello Sam, lots of posts on this forum. I'm assuming the alternator has its own regulator (not externally mounted) and the earth connection is through the frame of the alternator back to a high current cable bolted somewhere on the motor. I'm also assuming that when you connected everything up you did it correctly and did nothing to cause a spark.

If everything was done as it should be, and this is a new alternator then it still should be okay. Have you tried this. Run the alternator and then get a piece of spare cable and short out between the NEG terminal on the battery and the frame of the alternator while watching your charge light. This is a way of checking you have a good earth circuit.

Be warned that if the charge light goes out, indicating the alternator is working correctly, the piece of cable you are hanging onto will start to carry the charging current. Depending on the state of the battery (and engine revs) this could be well above the capacity of the cable.

HI Crusoe. Yes it has a built in regulator, but it apparently does not earth through the frame
I was told it probably would but when I tried it that way it wouldn't work, so I put an earth wire
on the post provided and it worked fine. The battery is approx 18 months old and in good order
I have heard it's easy to blow the charging diodes so as long as what you are suggesting doesn't
do that I'll give it a go. I definately had all power turned off when I connected it up so no spark
would occur. But I'm willing to try anything just to satisfy myself the system is OK. Thanks
for the info.

Hello Sam, if the earthing wire you put on the alternator goes directly back to the negative of the battery then the test I suggested won't be needed.

Just checking, in my very limited experience I haven't seen a designated Neg post on an alternator before. Is the earthing point you used on the alternator labeled for this purpose or is it just a stud/attachment point you chose? I ask this because I know that some alternators with internal regulators also have to option to be connected to external regulators.

Crusoe. when I received the alternator I took it to a local mechanic who used to repair these things (cheaper to buy a new one)
he showed me on the back of the alternator the spade fitting for the light, the post for the power lead marked + and a post for
the earth marked - he said it may earth through the frame but if not then to put a wire on the post marked - which I did and it worked.
So it seems that on this particular alternator there is a designated neg. and it is needed. What do you think.????

I'd say the mechanic should know what he's talking about. Me, I'm just guessing without seeing it.

Does not matter if the battery is fully charged. The alternator will always work the same. The alternator frame is the earth and must be connected to the battery earth. Some times this means a dedicated wire from the frame to the engine block and then the earth strap to the battery.

If the F light is on then goes out just after start up you should have at least 13.5v across the battery terminals. The alternator will output 60 or so amps for a minute or two then drop down to probably 20 amps or so as soon as the battery has recovered from the start.

If the light flickers at idle you may need to alter the pulley ratios to ensure the minimum rotation speed stays above 5000rpm

Thanks Ramona. All information gratefully received.