Date registered: Nov 2005
Vehicle: 1996 210.020
Location: Adrift on a continent...
Mentioned: 0 Post(s)
Quoted: 3 Post(s)
RE: Just bought a 1985 300D
Ask for cables for a '85 300D, of course. Yes, you'll need special cables, but that's a given for any car with an aftermarket head unit.
Note also that you have a fader control behind the shifter lever. Any aftermarket unit will have this built-in, so you may wish to disconnect that control and wire up the speakers directly to the head unit. Your call there.
I've not replaced speakers on a W123, but speaker installation is usually much more involved than head unit installation. If you found elements with the same form factor (physical size, mounting hole locations, etc) as stock, it would be quite easy.