I have a 1985 300D (123 Chassis) and am seeking information on installing an AM/FM/CD player in the place of the factory AM/FM/Cassette. The factory wiring is intact and connected to the original unit. The wiring consists of the 4 connector plug (Brown, Gray, Black, and Red), the antenna jack, only two pair of speaker wires, but there are 4 speakers (I suspect this is due to the fader control in the console), and of course a Ground.

Any advice from you experienced folks would be greatly appreciated.