My New Ride! Need help identifying a few things

[harpua00]

As of about 2wks. ago I bought my first MB diesel and I've been searching and lurking on this site since; it's a 1985 300D with 230K miles, anthracite grey outside with black interior. No rust, and in general seems to have been relatively well cared for, though there are lots of nagging "little" things that no longer work. Actually, lots of them! The car runs and drives well, though it need front brakes and rotors. Central locking does not work. Gear shift lever seems loose and probably needs new bushings in the linkage and the 2-3 shift is a bit dragged out under heavy throttle. Sunroof doesn't work, neither does radio nor antenna. Oh and the drivers seat leaves my left cheek about 3inches lower than my right. Yikes, listing it all makes me realize I've got some evenings to spend on this car. But, despite all this I am in awe at the quality of the car (which because of all the problems, my wife finds very amusing)....for a 23 year old car it is outrageously solid; you drive over potholes and railroad grade crossings and can tell the sturcture is very rigid and really from this perspective the car feels like new. Oh, and I love the sound of the engine!

So, 4 intial questions:

1.) What is the lever that hangs off the back of the sunroof motor?

2.) If the radio (oem unit from the looks of it) won't power on and all fuses in the fuse box are good, does that mean the radio is dead? Is there any kind of code or sequence of buttons that need to be entered after battery was dead for a while? How about the antenna.....should the dash switch operate the antenna even if radio is not powered on? i.e. do I need to first fix/replace the radio before worrying about the antenna? Finally, the antenna connector in the trunk has two "extra" small, loose round pin connectors. One wire is blue/yellow and one is blue/green. They currently are not attached to anything, where should they attach? See photo

3.) I see a disconnected and plugged vaccum fitting on the firewall just above the oil filter housing. See photo. The fitting on the firewall is a yellow plastic connector or valve of some sort, the plugged fitting is a 4 way Tee. What is this?

4.) Final question. I hear a very loud continous screech at very light throttle in 2nd, 3rd and 4th gears between 2000-2400rpm. At first I thought loose belts, but the above conditions are the only times I hear the screech and I can make the screech happen every time just by using light throttle under the conditions described above. Other than those specific times, I never hear the screech (i.e. never at start up, or revving the engine as you would expect for loose belts). I'm wondering if maybe it's a vaccuum leak, not a loose belt?

Thanks!

Mark