Duo Therm 5 button Tstat does not "see" new 2nd AC unit

I have downloaded and read everything on troubleshooting I can find from Dometic/Duo Therm for this set-up. I have cleaned communication jacks and cable ends with electronic cleaner, replace the communication cable ends from AC unit 1 to AC unit 2 with cable orientation to cable ends as detailed in troubleshooting guides. I have replaced the control box on the original unit, reset the Tstat multiple times and verified DC polarity at control box connection to RV DC supply (13.84 VDC). At the RJ 11 jacks, there is no DC voltage from Red to Black, (which is not what is expected per troubleshooting guides) but there is 12.75 VDC from Red to Green and 4.74 VDC from Yellow to Green when reading through the communication cable plugged into a standard household phone jack. The communication cable looking from left to right with the locking tab on the connector facing me is Black, Red, Green and Yellow on both cable ends. The original AC and furnace both work as expected, but the 5 button CCC thermostat does not show "zone 2". The RV was prewired for a second AC unit with a remote temp sensor preinstalled as well as a 20 Amp 120VAC supply circuit and a preinstalled communication cable. Dip switches on second unit are all off with the exception of Zone 2 (turned on) and all off on the original unit with the exception of the furnace dip switch (turned on). Please help, as I only have so much hair left; and what I do have is hard to get ahold of to pull out!