Brief update...and thank you all for the assistance:
My avionics-guru with Rob's help narrowed the problem down the the 430W or the ARINC interface, although the leading thought by most of you was that it was a wiring issue. So my buddy took the 430W out of his son's airplane and was going to put it in mine to see if it was the 430W. When he was pulling it from mine, he noted that the ARINC connector was sitting a little cockeyed and found that it was actually partially unplugged due to one of the securing screws being too short. He got a new screw from the avionics shop, plugged it back in, and everything now works perfectly except for the separate panel-mounted artificial horizon. It's kind of an ancient instrument, the company is out of business. We thought is was part of the wiring issue...turns out that it's just completely T.U. I ending up getting a good deal from Jason at Aerotronics on a G5 to replace it, which will give me good redundancy. Pleased about that.
Bottom line...ya'll were right. It was a wiring issue, now solved.
Thanks again.