W202 Battery Warning Bulb on dash not illuminating

[Ds24215605]

Good morning,

C230 2.4 Sport Automatic Petrol W202

I will try and be specific;

I have had a new battery and alternator fitted as expected the alternator was goosed.
After it was fitted i noticed that the Battery/Alternator warning bulb was not illuminating. (this could have not been illuminating prior to me renewing the battery and alternator hence the issue of flat battery!)
After a lot of fault finding by the Automobile Association it was found that the Alternator was not charging the battery but when it provided with a separate power source to provide excitation it was working fine.
He traced the fault to be between the D (Small) connection on the alternator and the dash light bulb. Apparently if the bulb is not working correctly it does not complete the circuit and excite the alternator on start up.

Action i have taken.

Removed the dash and fitted new bulbs (Correct voltage etc....)
Cleaned all connections.

The car starts fine but the battery / alternator bulb still doesn't come on or off? and the alternator is still not charging the battery?
Is there something else i am missing a fuse or something simple i have overlooked? I have checked all my fuses and they all seem to be ok.

any help appreciated,

Cheers

Derek

 

[whitenemesis]

I have had a new battery and alternator fitted as expected the alternator was goosed.

You had the work done or you did it yourself? If the former take it back and get them to sort it?

 

[Ds24215605]

Did it myself

 

[Ted]

Right.
There should be a thin (blue?) wire to the back of the alternator. With ignition on, engine not running, if this is removed and grounded the light should come on. If this happens and it does not come on when plugged in, the alternator is faulty.
You are correct, this provides the initial excitation. However this can be overcome by high revs, which should use the residual magnetism in the alternator rotor, and then it will (should) charge as normal until the engine is stopped.

If grounding the small wire doesn’t bring the bulb on I would be checking the warning light bulb or associated circuitry.

 

[optimusprime]

Check that the alternator plug is clean and no corrosion ,, and pushed fully home . Next check the fuse in the fuse box .

 

[optimusprime]

So with key on ,, without starting the car, you can see no bulb light up for the alternator . Just to get it right to start with .

 

[optimusprime]

The battery will never charge if the inciter bulb is not working . Could be in the console itself where bulb fits or may be a bad earth point thats in the chassis where console was removed from .There is an earth point down by the alternator ,,clean that and grease it up .

 

[Ds24215605]

Thanks,

by thin blue wire do you mean the connection from alternator (D Connection) ?

No light on when turning on ignition.

Where is the fuse for the alternator you mention? we have had a look but cannot find one.

Could the 2watt bulb be the issue that is in the dash assembly?

 

[optimusprime]

Did you replace the exiter bulb back in the right hole,, and not in to any other after bulbs were replaced You wont be the first to install the bulb holder in another location . Like in to a hole for abs ,,any way to check is are all the other bulbs working for other items when you switch on first

 

[Ted]

Yes. There will be two possibly red thick wires. Don’t ground them!! The thin wire can be safely grounded to test the bulb and associated wiring.

 

[optimusprime]

DS I would say check charging from Alternator . And all blue bulbs are 1. 2 watt large clear bulbs are 2 watts only some of the bulbs can be replace via pulling the bulb out of its holder . And if they dont work its the cluster, there is so much on that pc board to go wrong .

 

[Ds24215605]

Thanks for the advice so far,

waiting for new bulbs from Germany! But all the bulbs on the side of the Battery charger sign are working ok? just not the battery warning light?

Is the bulb connected to a fuse anywhere?

I have put a new bulb into the 2 volt on one side but waiting for a new bulb for the other 2 volt bulb which has blown? (the only 2 volt bulbs in a yellow housing) are these anything to do with the battery bulb in any way?

Ted, the AA guy said the fault was definitely between the Alt and the bulb.

 

[Ted]

Time to get a testlight out.
You should have 12v on one side of the bulb, and the other side should go to earth through the rotor and regulator in the alternator.
Did you disconnect and ground that wire? Did the charge lamp come on or stay off?

 

[optimusprime]

Getting confused here . So the exiter bulb is working but the battery warning light is not ,,yes ? Can you find your battery cable junction box .?

 

[Ds24215605]

Getting confused here . So the exiter bulb is working but the battery warning light is not ,,yes ? Can you find your battery cable junction box .?

Is the exciter bulb a different bulb than the battery warning bulb?

Battery warning light not coming on at all.

 

[optimusprime]

The exciter bulb are normal bulbs as far as i can see . But until your bulbs come we wont be able go any further . You need a wiring diagram for the dash to see just what bulbs do what ...I dont know you are the only one that can check them ..As for that fusable link its on the battery post lift up the red cover to expose the fuse link .

 

[wrdcc01]

Ted has outlined the way it works and how to test it. That's all there is to it. Either the lamp is buggered or the wire from the alternator to the lamp or the voltage regulator which the circuit feeds through to earth. This earth changes to positive as the alternator starts charging and produces an equal potential across the lamp which turns it off. If you earth the blue or blue white wire from the alternator to the lamp with the ignition on it should light (earth it at the alternator end) If it lights the alternator has an issue, if not it is the wire or lamp. Run a jumper to the lamp to prove.

 

[Ds24215605]

Sorted, the area around the bulb holders where the bulbs plug in has somehow become loose so the bulbs didn't sit tight into their sockets.

Not sure how that has occurred?

Bought a second hand dashboard unit fitted it and all works ok. I will keep the old one spare just in case.

Thank you all for your help.

Much appreciated

 

[optimusprime]

Nice to know you found the culprit after all .

 

[John757]

I had the same bulb go on my W460 G Wagen, I had no idea it was so important until I broke down.. AA man lent me a new battery and followed me home.. diagnosed a faulty alternator... took the alternator off and had it tested, the tester man said its fine... when he asked me about my battery light bulb and I said it was blown , he explained how this is an essential part of the charging circuit.. then the light in my head illuminated! he sold me a new bulb for a few quid and everything was fine after a full battery charge....
Perhaps there should be a warning light for the battery warning light!!