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Old 19-03-18, 08:02 AM   #1
krzracingcouk
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Default Battery light not going out.

i have posted this on Facebook too to see if anyone can shed some light:-

I have a '82 Coupe GT 5s, when I start the engine the battery light stays on normally for a while (not sure if right for this age of car) on that day but every start after that goes out fairly quickly (about a minute or so) and the voltage on the volt meter from about 11v to 13v ish. The other day the battery light did not go out and the battery went flat on a drive.
I have changed the alternator for a different one and put a meter on the battery and voltage does go up when engine is running but battery light stays on and VDO gauge does not agree with meter directly on battery. Is there some relay that is playing up somewhere? Is there some checks I can do to see what is not working? Have also wondered if it is worth running a ground lead directly from the body of the alternator to the -ve of the battery?
I look forward to any help.
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Old 19-03-18, 08:56 AM   #2
Colin Aitchison
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I am no expert on alternators, but if the light is on the battery is not charging, you original alternator sounds like the carbon brushes have worn out, this dose happen with old cars and old alternators, you can normally replace the carbon brushes but the norm is they come attached to the voltage regulator, the voltage regulator is normally at the back of the alternator fixed in with 1 or 2 screws, a we bit tricky job to do on the car but can be done as I have done it on the Ur quattro, after fixing the the Ur quattro voltage problem I did order a spare voltage regulator as one of my other cars has the same alternator, photo below of spare voltage regulator, this may not be the exact same part as yours but may be similar, the two carbon brushes are at the top of the photo and are on springs, yours will be a lot shorter as the springs push the brushes against the alternator shaft and they wear till they lose contact and battery dose not charge, as for cost £10-£20, no comment to make on you second alternator problems.

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Old 19-03-18, 09:02 AM   #3
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Sounds like the replacement alternator is faulty? If you remove/disconnect the small wire from the alternator and the light goes out then alternator has an issue. If light stays on then suspect wiring or problem behind clocks/dash.
If engine cranks ok then I'd not worry about adding a separate earth lead, just make sure the alternator is secure and earthed to bracket/engine.

Does the B2 have a flashing oil warning light like mk1 Golf?
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Old 19-03-18, 09:12 AM   #4
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Morning John, very nice reply, with wire testing, need to keep that test in my mind but will need to push some other crap out, but what to push out Hmmm, Sorry, I have had 3 cups of coffee and can't stop typing, Have a nice day.
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Old 19-03-18, 09:14 AM   #5
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Quote:
Originally Posted by Colin Aitchison View Post
Morning John, very nice reply, with wire testing, need to keep that test in my mind but will need to push some other crap out, but what to push out Hmmm, Sorry, I have had 3 cups of coffee and can't stop typing, Have a nice day.
I NEED 3 cups of coffee !
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Old 19-03-18, 09:38 AM   #6
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Are you sure the alternator you put on works ? you post suggests it's not new ?
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Old 19-03-18, 07:44 PM   #7
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Hi guys,

Thank you for your replies, I will try and answer all you points.

Colin - Changed that on the old alternator and no difference

John - With the D+ wire connected or disconnected the light stays on.

I have been told by someone else there should be a voltage between the lead that goes to D+ and ground but when I put a meter over it I get 0v with ignition off and 0.05v with ignition on. So I am guessing that is the problem - if so does that track back to a relay or what?
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Old 19-03-18, 08:30 PM   #8
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Quote:
Originally Posted by John. View Post
If light stays on then suspect wiring or problem behind clocks/dash.
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Originally Posted by krzracingcouk View Post
John - With the D+ wire connected or disconnected the light stays on.
Sounds like you have a problem that isn't the alternator.........I was asking about the oil light as I remember on mk1(and maybe mk2?) Golfs that there's some electronic trickery built into the dash clocks?......maybe this could be your problem.....I don't know how you'd test this, probably easier to install a set of clocks that are known to be good?

Maybe worth-while checking all connections and earth points around dash area as it could just be that another circuit is earthing itself via the battery ind circuit??

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Old 19-03-18, 09:42 PM   #9
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I guess I know what I am going to be doing for the next few nights now

Just hope I find it quickly, wish me luck
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Restoration Thread

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Old 19-03-18, 10:15 PM   #10
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Well, first of all - you say that "multimeter on battery doesn't match reading of VDO voltmeter" - what's the reading of both? If gauge shows some quarter volt below voltage on battery, that's normal, as there is some voltage drop between battery and gauge. The only question is - how good is your alternator working?

If you can remove exciter wire from alternator, and alternator light keeps shining, apparently exciter wire is grounded somewhere - but alternator self-excites if it's being revved behind some threshold; let's say, if engine is revved past 3k rpm - just for your info, if you continue to drive the car without this problem being solved.

As for "electronic trickery" John is speaking about - in order to rule that out, you can remove oil pressure warning relay - in VW's it's in cluster itself, but in audis of this age it's separate relay, must be above drivers feet [at least in LHD cars], with "õl druck kontrolgerāt" written on it, if you remove it, that removes oil pressure warning [both buzzer and light], but if that restores normal behavior of battery light, you'rs is faulty.
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