Sorry for the long post, I hope I can get some help to save some debugging time. I'm new to MB/diesels and am still learning. Also thanks in advance for any advice!

1. Rear window defroster – When I click the button to turn on the rear window defroster, the light in the switch brightens up and eventually goes back dim. Problem is, the rear window is still fogged up. It has never worked since I purchased the car about a month ago. I have gone in and replaced all fuses, hoped I might get lucky with an easy fix. Any suggestions on a place to start debugging?

2. Wobble @ take off – sometimes when I start driving, the car seems to wobble back and forth a little. Once I get a little speed, the wobble subsides. Any ideas on a cause or should I just not worry?

3. Sound from under rear of car – When I let of the accelerator peddle I hear what I can best describe as a rubbing/grinding noise. It is not loud, if I have the window open or radio on, I cannot hear it. I do not hear the noise as I accelerate (as best one can in a 240D ). Again, any ideas?

4. Cruise Control – I have searched and found much info on cruise control issues. I would still like to put this question before the user community. When I got the car, I pressed the cruise lever to engage the cruise the first time. The car accelerated, but would not hold speed. The next time I pressed the lever, nothing happened. Later, I had the vales adjusted. I decided to try the cruise again. Accelerated and would not hold speed. All tests between my first test and since the valve adjustment result in, nothing happens when I press the lever to engage/accelerate. And I know it is a 240D and I’m sure it’s not accelerating!

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1981 240D, Auto Trans, 160k miles -- CRASHED!

To start you off I believe #2 and #3 are related.....please check it out ASAP as you likely have suspension issues that could be dangerous.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

The rear window defrost is powered through a time dely relay. It is supposed to turn off automatically after 30 minutes. I suspect that your relay has lost track of time, and is turning off early. The relay is located behind the instrument cluster. (The defrost relay is on the left, window rely is to the right. Both are silver "cubes".)
A reread of your post leads me to a question. How long is "eventually?"
Power is routed to the rear window defroster through a 14-pin connector located near the parking brake support under the dash. Check for power at pin #1 (black wire.)

The wobble you are feeling could be from a tire that has developed a bubble from a pothole. A bubble develops when something disrupts the tire plys. Obviously a dangerous situation as pointed out even in a vehicle out run by a well pedaled tricycle. This is definately a case to take to competent mechanic or tire shop.

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Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)

I tracked how long it took the rear defroster light to dim back to normal, it was right at 25 minutes. I will check the connection for power.

Thanks.

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1981 240D, Auto Trans, 160k miles -- CRASHED!