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My wife noticed that the ABS light came on this morning but the ABS worked fine. She left the car with me and I was unable to replicate the problem but checked the output across the battery terminals and it ran 15.8-16.1 volts. The manual mentions that it should be 13-14.5 V at 3000 rpm. with no more than a 12.7 V drop with all accessories on. I maintained 16V with or without a draw. In a previous post, our moderator suggested the voltage overprotection relay as a potential trouble spot for a long cranking cycle problem. I'm wondering if failure of the relay could be the reason for the high voltage or if the voltage regular is going TU. I really don't want to fry my battery. Given the price difference between the regulator and an entire alternator ($188) should I hedge my bets and put a new alternator in my 98K 400E? I hate to just throw money at it, but I do all my own labor and have limited time. I don't want to play with it, just fix it. Anyone have a similar experience :?:
 

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I would say that the regulator is fried, and the battery will cook. As far as the fix or replace option, I recently tried to fix mine and only ran into more expense (likely due to a faulty new regulator). I ended up replacing the entire alternator anyway. It was very frustrating because, like you, I do my own work and time was essensial.
 

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16V might be normal?

Thanks for the input, I’ve visited the Bentley Web site and their take is that “new type” batteries with more cadmium in their construction require a 14.5 or better charging rate to keep the batteries up. They debunk the notion forwarded by “the industry” (car manufacturers and battery makers) that it is necessary to keep charging systems operating between 13-14.5 V as inadequate. As I read it they consider the old hoary conventions too conservative and not in keeping with the requirements of modern battery construction. They do recommend not charging beyond 16.5 V or you run the risk of boiling the battery dry. Right now, I’m watching things. If the battery (a gen-u-wine MB battery, courtesy of the PO) looks like it is running to the dry side, I’ll replace the alternator. At almost 100K it’s one of those things that is likely to die when my wife is driving the car, with subsequent repercussions.
 

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Well, I sit corrected! I guess I also misinterpreted your "12.7 V drop" statement, but that is also my bad. :oops:
Keep us posted on how this works for you!
 
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