Car wiring diagrams: 3M Intercom System Wiring Diagram, wiring diagram, wire wiring harness, schematic circuit diagram, wiring diagran, wireing diagram, wirring diagram, wiring daigram, wiring diagrams. Refer to Figure . The optional M A Noise Reduction board M part number improves the inbound intelligibility of an intercom system .Intercom System M Convenience Store D Installation Instructions Manual. Intercom System M DA D Installation Instructions Manual. Wired Intercom System Performance Series Models Installation Instructions .M Wireless Communication System Model XT . Installation . the Installation. There are multiple ways to install the intercom system. Before . use this wiring diagram for each of the stations, then see "Base Station to Base. Station Wiring .