I just finished upgrading my sound system in the 83' 300D. Figured I would post all the details to help those who are looking for what fits and how to bypass the factory fader.

I went with a Sony CDX-GT610UI cd player because of the included IPOD cable and USB port on the front face. For the front speakers I had a hard time finding anything to fit under the factory grills becasue the tweeters on most speakers protrudes too far. But, a pair of MB Quart 4" DKE 110 will fit nicely with a little grinding in the dash opening with a dremel tool. The MB's give you the option to attach the mounting ring to the speaker from the top or the bottom. If you attach it from the bottom there is just enough room, once you grind the stock hole in the dash so they sit flush to the top of the hole. The factory grill fits on nicely. For the rear I went with a pair of Eclipse SE8355 5 1/4". They fit into the existing hole but you can't use the stock covers, you have to use the ones that come with the speakers.

Now to bypass that fader. Remove the radio, ashtray, glovebox and panel over the gear shift.

Front Right: Find the speaker wires behind the glovebox. One green/black and one black. Follow that down to the area behind the radio.

Front left: In the area behind the radio find the black/red and black. It's coming out of the same cluster as the wires for the front right.

Rears: To the right of the gear shift you will see two plastic "plugs", one is black and one is whitish. They are labeled "R" and "L". Coming into them are green and red wires. Coming out are 4 wires, a brown/red and brown and a black/green and black which all go into the same sleeve that heads to the back. When you remove the left rear speaker you can see the wire harness that I just descibed. The Brown group is the left rear and the black group is the right rear. The ones with the stripe are positive.

Good luck, and I hope this helps somebody!

that is sure to help many..