03-09-2004, 07:50 PM
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Registered User
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Join Date: Jan 2004
Posts: 42
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Quote:
Originally posted by blackmercedes
You need a helper. With the car running and the headlights on, sit at idle and check the intensity of the lights. Rev the engine to 2500 or so and see if the lights brighten at all. If not, then you have a charging problem as the increased current from the alternator once the threshold rpm is met should juice up the lights a bit.
Static voltage on the battery won't tell us much, not the way load testing will. But, there is a quick way to tell if you have a key-off drain, and that is to disconnect the battery and leave the car overnight and recheck the voltage. If you undo the positive lead, please be VERY careful not to allow your wrench to touch ground while working on the positive terminal.
I still think it's a charging problem. Why?
We had the same problem with our 1990 190E and the idiot dealer kept chasing a key-off drain. After three full months of mucking about, the alternator finally gave out. It was slowly fading away and charging intermittently. The dealer would test it and it would read 13.7 evey time, but we had dead battery problems. Now, to the credit of the dealer, the alternator tested okay when they had it. However (I had sold the car to Dad at this point) they insisted that it was the power antenna draining and charged him $500 for a new unit. Cripes. Anyway, one day the alternator finally calved. I put in a new brush set and it's been fine since. $60...
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I'll be back in a few, I'll go do your test.
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