An update to my last post, I now have the interface working properly, talking to the TIU and all is well. It turned out my problem was the wires in my handset cable are not exactly in the same order as they are in Mark's photo of his cable. Once I figured that out all is well. The attached photo is of my version of the interface breadboard.
Yes Yellow and Green are switched from the schematic because they are switched in my handset cable.
