The port settings are located under the AppleTalk screen in MPM. There is a pop-up menu for each LocalTalk port. Choose "Serial Connection"
Conceptually, think of the ARA zone and network number as being a fifth phantom localtalk segment with its own network number and zone name. Well, this is where the ARA users will be entering the network and this is the default zone the ARA users will see in their chooser
When the MPM looks for CCL files, it will look for them in the following order; if it finds at least one, it will not look any further.
After this, MPM will not look any further.
Usually it is a sign that the modem cable in use is not a Hardware Handshake cable. Most of the time, the cable that came with the modem is setup for hardware handshaking, but even then, they sometimes still get it wrong. In selecting the correct modem cable, look for the wording "Macintosh Hardware Handshake Modem Cable" or "Mac to High Speed Modem."
Below is the correct wiring diagram
MP/LT user Reference v2.0 p19 table 2-4