We are chasing down a missing zone 2 problem. Have seen several of your posts about the comm cable being the problem. My husband is in the middle of building a new cable to try to pin down the issue. Being an electrical engineer, he is wanting to know what the 4 wires of the comm cable are used for. Understand the black and red are for power. How about the yellow and green? Any help would be appreciate so I can stop trying to find this info. Thanks.