Three days ago, this came on upon starting up. It goes out at 4500rpm, but comes back on once the revs drop again. Both times I have taken it out more than ten minutes at a time it goes completely after giving it a rev.
I have checked the belt tension, seems okay, so its either the wiring or perhaps the alternator is sticking until it warms up a little.
Any ideas?
Steve
Charge Light (Battery symbol)
alt
I would check the voltage across th ebattery at about 1500rpm it should read approx 14v if it doesn't then the alternator is not delivering enough so it may be faulty or it could be a slipping belt or pulley - the 16v alternator pullys are known to be rathe rweak when old.
Cheers
Luke
Cheers
Luke
Please call me Luke 
1989 BX 16valve White 70k almost up to scratch
1989 BX 16valve White 70k almost up to scratch
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Timmo
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had similar on my old 8v pug! turned out the alternatre had had enough:( as luke said get a multimeter on there to check your voltage with the engine running! also check the spade plug connection on the alternater (single wire) as iirc that controlls the light!
Timmo 
After all i am the Cornish one!
Its Because its French!
Bx16v club - Sharing the love for the unloved!
After all i am the Cornish one!
Its Because its French!
Bx16v club - Sharing the love for the unloved!
if the light is coming on then it is earthing through the alternator regulator, which happens if there is an electrical fault or if the regulator is failing. The fact that the light is coming on and going off tells you that the wiring to the alternator is fine, so its going to be something up inside the alternator.
This can be either a faulty regulator, insufficient stator current or lack of generation from the alternator usually caused by worn brushes. Regulators normally fail where by they go over voltage and everything becomes brighter and the light stays off, in this cause if the regulator has failed then it isn't allowing enough current to be generated and get up to 12v (once the alternator output is at 12v the light will go out), in this case once the light has gone out and stays out check the voltage. If its around 14v the regulator is okay, but it is rather likely that the voltage will be just above 12v!
To check stator current, with the ignition on and the engine not running (battery light should be on) put a meter between the wire going to the small wire on the alternator and ground on the battery, this should be 11v or higher.
The likely hood is that the fault lies with the brushes, if they are right at the end of there life, then as the copper core of the alternator warms up it will expand and make better contact with the brushes thus the light stays out until the alternator cools off again. However all is not lost! First get a high pressure compressed air gun and blow the alternator out (through any available aperture, but remember the brush dust that might come out is carcinogenic (NOT VERY NICE)), sometimes a build up of dust from the wearing away brushes causes short circuits! One of the biggest causes of failure for this type of externally cooled alternator (fan on the outside) is caused by overheating! So if the brushes are totally dead you can have the alternator re conned (last i asked it was about £40 and only the external fan variants, are done by most places), you can try to buy the brushes (i have seen a site recently that supplies them for this alternator, but don't remember what it was) you can buy a totally refurbed unit (that has new brushes, regulator and paint job) or you can simply buy an entire new unit. These later options obviously start to get a bit expensive very quickly!
Now, getting the alternator out is a whole other topic, i'll let someone else tell you about that!
This can be either a faulty regulator, insufficient stator current or lack of generation from the alternator usually caused by worn brushes. Regulators normally fail where by they go over voltage and everything becomes brighter and the light stays off, in this cause if the regulator has failed then it isn't allowing enough current to be generated and get up to 12v (once the alternator output is at 12v the light will go out), in this case once the light has gone out and stays out check the voltage. If its around 14v the regulator is okay, but it is rather likely that the voltage will be just above 12v!
To check stator current, with the ignition on and the engine not running (battery light should be on) put a meter between the wire going to the small wire on the alternator and ground on the battery, this should be 11v or higher.
The likely hood is that the fault lies with the brushes, if they are right at the end of there life, then as the copper core of the alternator warms up it will expand and make better contact with the brushes thus the light stays out until the alternator cools off again. However all is not lost! First get a high pressure compressed air gun and blow the alternator out (through any available aperture, but remember the brush dust that might come out is carcinogenic (NOT VERY NICE)), sometimes a build up of dust from the wearing away brushes causes short circuits! One of the biggest causes of failure for this type of externally cooled alternator (fan on the outside) is caused by overheating! So if the brushes are totally dead you can have the alternator re conned (last i asked it was about £40 and only the external fan variants, are done by most places), you can try to buy the brushes (i have seen a site recently that supplies them for this alternator, but don't remember what it was) you can buy a totally refurbed unit (that has new brushes, regulator and paint job) or you can simply buy an entire new unit. These later options obviously start to get a bit expensive very quickly!
Now, getting the alternator out is a whole other topic, i'll let someone else tell you about that!
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Anonymous
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Timmo
- Full Throttle
- Posts: 2233
- Joined: Tue Jun 27, 2006 3:30 pm
- Location: Cornwall! Tis where they make Oggy's!
- Contact:
nice one steve! you want to try it down here mate! just popped downt he beach for some photo's! that bl##dy windy even the antishake couldnt help me get the photo i wanted loL! do now have a nice sand blasted face though! 
Timmo
After all i am the Cornish one!
Its Because its French!
Bx16v club - Sharing the love for the unloved!
After all i am the Cornish one!
Its Because its French!
Bx16v club - Sharing the love for the unloved!