ML430 CD changer complications

[maxus]

Hello, thanks for any help in advance.

Bought a used MB-branded CD changer for my 2001 ML430. The truck is pre-wired for a fiber optic changer. The changer has what seems to be compatible connector slots. After hooking it up to the truck wire harness, the MCS does not recognize the changer. The changer powers up, ejects the CD cartridge, but does not communicate with the MCS. Is there anything I should be doing to let the MCS know the changer has been installed? Is there some kind of a procedure?

2001 ML430, production date 9/00.
2001 CD changer MC3110, part # A1638201589

Any advice is appreciated.
- Max