So I pulled the Nav unit, APIM and amp from a 2012 E250 today. Pertinent numbers:
ACM: ****-18k931-ba
APIM: dc2t-14b428-aa
AMP: ar3t-18t805-aa

Now I'm attempting to bench test this setup.. so the radio, sync module and amp are connected together. Using a 13vdc power supply all I get on the radio/nav unit is a black screen. The only buttons that cause any actions are eject and the vol push (inner part of the lefthand ****). Pressing eject sits there for about 2 second then the screen backlight comes on and it displays 'no disc' for another 2 seconds before going black again.
The vol/push button does the same except once the backlight comes on nothing is displayed, so 2 seconds of black, 2 seconds of backlight then back to black.

My question is, does an ACM/APIM require a CAN bus connection to really do anything?

the only wires not connected to anything are,
ACM: White/Violet
Blue/Orange
backup cam
APIM: Microphone
White
White/Blue

Thanks for any help/advice!