After looking at the images you posted I realize this is for your 92 500E (124 chassis, duh!).

Yes you will need the radio code.

This is a 2 piece radio, the tuner/receiver is in the trunk, this is where you will need to reconnect speakers (and hope things aren't too hack'd.

To install the head unit, I have wiring info, should be pretty straightforward.

You'll notice the one white connector with the metal tab on it, there is a tab on the bottom of the back side of the radio, that one connects there (I know I saw the wire for it in one of your images).

The one connector with the 4 wires going to it, just connect to the radio in the correct spot. The brown wire is gound, the black is power from fuse 1, the gray w/blue stripe is illumination, the red w/white stripe is power from fuse 9.

The other connector I believe is a 2 wire, the gray w/yellow stripe is the speed input for the variable speed-dependent volume control, the black w/yellow stripe is a mute signal for the factory cell phone.

I believe the tuner amp in the trunk is on the right (passenger) side. Hoping everything is still installed and you can just patch wires together.

On the back of the radio itself there is a small metal box, you should be able to find the connector that plugs into that as well, that's the data feed to the receiver-tuner.

Gilly