On my 83 300SD, I believe I need to change the voltage regulator. My dash warning lights don't light up unless I tap on a very small metal retangular box on the rear/top of the alternator. That and the battery drains (battery warning light comes on very dimmly when engine is running).

I do clearly see the voltage regulator further down on the back of the alternator (brush internal type). But, I don't know what that small rectanglular box is (screwed down to the back of the alternator on one end and what looks like a wire coming off the other end....looping down the back of the alternator). Since tapping on this box changes what the warning cluster lights are doing (on/off)....I would assume that is the problem. But, other posts say similar cluster warning light issues = voltage regulator.

So, what is that retangular box and do I actaully need to take off the alternator to replace what I know is the voltage regulator?

300SD has OM617 engine..check out this thread..specifically post #4...Voltage regulater replacement?

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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
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The "box" that you are tapping on is a capacitor (condensor), to help prevent alternator "whine". Tapping it probably is vibrating the brushes in the regulator and making better contact temporarily.

Replace the regulator and leave the condensor alone (well, check the screw and terminal tightness). Regulator is EASILY replaced with the alternator in the car.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Well, I got the new voltage regulator in the mail late yesterday with about an hour before dark.

All I had to do was crawl under the car with a stubby screw driver (didn't have to jack it up). Went to the back of the alternator, took out the two screws holding the voltage regulator in, slipped out the old one, slipped in the new one (wriggled it around to make it fit), and screwed the two screws back in.

The "brushes" on the old regulator were worn all the way down. When I got back into the car to start it, the dash lights didn't work the first time I turned the key, but I started up the car and the alternator light was on pretty full. Remembering from other posts I "revved" the car a couple of times. The battery light went off and when I turned off the car to check to see if the "dash warning" lights worked and they did. After driving around the car and stopping here and there, everything works great!

Good deal, I did mine about a week ago. To verify it's OK now, check the voltage on the battery with the engine running. It should be about 13.5-14 volts.