The M1XRFTWM Must start at address #2 and you can add a total of 4 M1XRFTWMs to the M1 Data Bus addresses 2,3,4,5. If you have the an M1XIN at Address #2 it must be readdressed higher in the list and those zones reassigned. If you Only have One M1XRFTWM it is OK to have the M1XIN at Address #3 BUT you will not be able to assign a Wireless Group 3 (Zones 33 – 48)