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The Alternator Light, what does it mean when...[200/1983] posted by Ugly Duckling on
Saturday, 16 December 2000, at 5:11 p.m.
My idiot light came on for my alternator (the battery icon), but the weird thing is that it lights up only after the key is out of the ignition. It goes away when I start the car, strange. What does it mean when the Alternator light stays on when you have the car in park and keys out? Thanks.
Re: The Alternator Light, what does it mean when...[200/1983] posted by abe crombie on
Saturday, 16 December 2000, at 10:42 p.m.
You have a bad diode in the rectifier set. Unplug the small gauge red wire from back of alternator and light will go out if this is the fault. You will need a rebuilt alternator.
These diodes convert ac current to dc current. If one of them is faulty then the current from direct battery connection to output wire on alternator is being fed to the exciter circuit in alternator where the alt warning wire attaches. When the key is off the feed is illuminating lamp on dash. Once the engine starts the alternator is still charging approx 70% capacity and you may not have a noticeable alt light (bet you can see dim alt light if you turn off dash illumination with headlights on with eng running). The alternator will keep up as long as you don't have alot of items all on at the same time but it will not last much longer as the extra current flow on the other diodes will tax them to the point of failure in time.
Re: The Alternator Light, what does it mean when...[200/1989] posted by Carl Bonner on
Saturday, 16 December 2000, at 11:13 p.m.
That's interesting. I have a similar problem. The alternator light comes on occasionally while I am driving. Never for as long as a second fully illuminated though it will be partially illuminated for 5 seconds or so then go out. It doesn't seem to be related to the length of the drive nor is it periodic. I can go for two to three weeks with no problem and then experience it for a couple of days. Never had a problem starting or operating the car in any other way, though. What could be the problem? Is it a symptom of greater problem?
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Carl Bonner 1980 240DL 158k, 1989 240GL 187k
Re: The Alternator Light, what does it mean when...[200/1989] posted by abe crombie on
Saturday, 16 December 2000, at 11:28 p.m.
If it's intermittent then this may not work if it is not actually lit up when you test: attach a voltwmeter set to AC scale and then run engine with some electrical load like headlights turned on. The AC voltage should be less than .050 V (50 millivolts) if the diodes are healthy.