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Old 05-23-2002, 04:30 PM
Village Idiot
Posts: n/a
Alternator or Voltage Regulator Bad?

Very strange things happening with my 85 16V. When the car is running, everything is fine - battery is being charged - all electrical works ok. But...
When I step on the brake the voltage meter drops, if I turn on the lights, the voltage meter drops - this is not draining the battery car still starts everyday unless I let it sit for over a week - then I need a jump.

The other problem I noticed the other day, I shut the car off completely and removed the keys from the ignition. My wife forgot to put her window up and when she hit the button, the window went up??? How can the window be put up if the car is off. This only happened once but makes me think I have a bad diode. What should I do?

Village Idiot

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Old 05-23-2002, 04:58 PM
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,596
Village Idiot,

I can't answer your question on the window working with the power off, as I have a Euro model with hand crank windows.

My 1986 190E 2.3-16 has the little Voltmeter in the three guage cluster in the console too. The needle flicker you see when you step on the brake or turn the lights on, or turn the blinkers or 4 way flashers and so on, is pretty normal in my view. The Voltage regulator needs a fraction of a second to respond to the demand for power, and in that instant the Voltage droops slightly. While driving, it is normal for the Voltage to be a little lower the more things you turn on, but not go below the 13.4 or so Volts you should have with nothing running at idle. The droop and needle flicker may be more pronounced at idle, as the alternator and regulator have no other parameter to work with to really balance the load. At higher rpm the alternator can make more juice and the regulator can keep things balanced at a more favorable Voltage. I see these effects all the time and my car has 206,000 miles. The head was recently removed, refurbished and put back on but we have a few items left before it will be running. Expect that this weekend. So, I can not recall exactly how much the Voltage droops or what the readings normally are at the moment, and also can not go out and turn it on to check.

I have used three batteries in the 16 years I have owned the car. I replaced the original one (Varta) at about 7 years, with the next (Sears Die Hard) lasting just over 5 and the one in there about (another Sears Die Hard) two years old now. I did have a defective Sears Die Hard last only a few months, but it was replaced free. So far, no issues with the alternator. Good Luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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Old 05-23-2002, 08:55 PM
Registered User
Join Date: Sep 2001
Location: central Texas
Posts: 17,277
Well, no wonder strange things are happening to your car..., your not supposed to be running 16 volts in it...When you step on the brake hold on to the volt meter with both hands or put it between your knees... dropping a volt meter is sure to kill it one day.... Where did Chivalry go, why are you not putting up your wife's window instead of making her do it ? Yes, you should shut the car off completely before you remove the keys.. in fact I can not figure out how to not do that...
UH,,, someone is talking to me in the background.. what ? OH... 16 Valves..... UH, Nevermind...

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