Thanks Bob. That clarifies the issue.
I also received a call from Marc Ausman this morning, which was a pleasant surprise. He explained a few more things that were not clear to me. Apparently the software that shows up on the HX is on the VP-X Pro and shows up via the serial link. My serial link is not working which is why I'm not seeing any software. The counter is showing no data passing between the two units.
Marc seemed to be leaning toward the fact that I've mis-wired this connection. When he called I was certain his guess was reasonable but nonetheless wrong. The diagram I used to figure out the pin numbering layout was a male 25 pin d-sub shown in one of the GRT manuals. Looking at the side the wires go into, and orienting the connector with the wide side at the top, the #1 pin is at the top right and 13 is top left, 14 bottom right and 25 is bottom left. I just looked at a pinout diagram of a 25 pin d-sub and darned if I'm not 100% right and wrong at the same time. What I described is perfect for the male connector. The female connector mates to this so the socket side would be identical - and the wire side would have pin 1 at the top left, 13 at the top right, 14 bottom left, and 25 bottom right.
It never occurred to me that the numbering scheme would be different for the male and female sockets. In short they're mirror images of each other so the pin numbers stay the same on both sides of the connector. Here's an image that explains it.
http://www.google.com/url?sa=i&rct=j...88782749530523 I'm at work now but this evening when I go home and move 3 wires on my J1 plug, I'm willing to bet the units are going to talk to each other (pins 20 and 22) and my AHRS is going to see 12 volts (pin 2).
I think it's getting very close to time to exclaim "duh" followed by a head slap. Someone on this board signs off with 'smart people do dumb things all the time' and I think I've qualified for this. I sure hope I've found the problem.
And lest I fail to mention it, Marc was kind and patient all the way - he must get tired of dealing with stupid stuff like this - his kindness means a lot - he could have made me feel pretty stupid…which is a about where I am on my own!