Alternator problem Cabrio 2001 AGG Engine

[fazersix]

I had an problem in March 2012 where the alternator warning light was "dim" when driving and not charging. I removed the alternator had an Auto Electrician test it and said it was charging ok. Forum advice was to check the indicator light wiring. I put the alternator back, checked the indicator light connections and the the alternator was charging fine around 14volts.

14 months later, same issue. Alternator warning light was dim when running battery discharged and wife was stuck! I removed the alternator to get it inspected again and then read an article on testing the warning light. I put the alternator back in with a few taps to get it into position, switch the key on but not starting the engine, warning light was on - good. I disconnect warning light from back of alternator and grounded it - light on also good. I then connected it started the engine and alternator was charging at 14V. Whilst enginge was running and alternator outputting 14V tested voltage between battery negative terminal and alternator body 0.2v - article said less than 0.5 V is good!
I am now guessing that there is an intermittent fault in the Valeo alternator and am thinking of replacing it with a Bosch unit or refurb the Valeo, but probably not economical. Car is 2001 2.0l Cabriolet AGG engine 185,000 km's
Any advice appreciated.

[Jmac]

Please test the voltage from the D+ wire which is the small blue one on the alternator, not the large battery cable as most do. This is what tuirns the light off and will give the voltage at which the alt is putting out. The 0.2v you have checked is the earth which is correct. Check it at idle, check it with consumers on and sometimes you will , in your case most likely have to go for a drive with the multi connected up, extend the leads, go for a drive and watch that D+ puts out and observe as much as you can. Seen it before where itll check out good and then intermittently drop whilst driving, different loads etc certain rpms etc, hope that makes sense, seen it before many times been checked by sparkies and still ends up being the alt or at least the reg.
Good luck
Jmac

[fazersix]

Thanks Jmac I will certainly check thus out, it will take some time. I guess since it is working fine now tests will be ok, I am thinking of installing a voltmeter to monitor when driving to see if it is an intermittent thing where the output drops below 11v so car is running on battery but light doesn't light up. Am I right un saying that since the light is connected to D+ when voltage on D+ is 0 light glows cos circuit is complete. When greater than 12v no light cod " open circuit" But in my case (guessing) output drops to a lot less than 12 v and light is dim due to "partial" circuit completion. So I understand reg could be faulty but what about diodes?
Thanks

[fazersix]

Problem fixed. The bushes were worn so spring pressure was not enough to stop them from sticking.
Sourced a replacement regulator with brushes from ebay Uk for $20 problem fixed