Here is the problem I believe you'll run into due to the way its wired currently: without the rear PTT wire going to the intercom there's no way to trip the relay to enable the rear headset microphone.
Thanks Chris, it does make sense for sure. I wish you lived in our airpark! I did run a jumper wire from the white wire to the blue/white and when I grounded it the tx on the radio work I thought I had success but no, no sound in the headset, so that is when I called Sigtronics and found out my radio is not compatible with the intercom without the relay added in the circuit, damn I thought I had it for sure. I wish I could somehow send you the keyline modification schematic they sent me so you could see what I have to do. I would change out the unit, but when I look under the panel and see bundles of wire I panic, it might be just above my pay grade.
Chris finally got it, what should have been a 3-hr. job turned into a week project. After talking to Sigtronics it turns out the intercom being 12V and the I-Com 220 radio internally is 7V it would not handle the second PTT switch. It did handle one, but not two. And the guy that installed the new radio and intercom had it wired very different than the schematic, being a voltage thing, I guess, but the front PTT did work. So, I had to pull most the wire out and the radio out to get the right pin locations and splice in a 12V relay in line from the #5 white wire to handle the voltage difference from the intercom to the radio. Rewired the whole system per Sigtronics, after all that it works great. The voltage was the problem and my luck the I-Com 220 is the only radio out there with that problem. Thanks for your help along the way!
