Update: The AR 9210 tested good at HH. They had to provide all the wiring and attachments, etc as all I sent was the main unit. Consequently, after my close inspection of the involved EC3 to MPX adapters, I have come to the conclusion that possibly both MPX connectors must have not been making consistent contact. ?? Some of the female pins in the MPX side of the adapters were spread apart, some of the pins were made from thinner metal, & some of the pins were in the molded plug further. I replaced the EC3 to MPX adapters. The new ones looked a lot better and took a lot more pressure to fully seat and get "clipped in." Also, instead of mounting the AR9210 as suggested in the book, I sandwiched a piece of 1/4 receiver foam between two plywood boards and mounted the AR on top of that. I also ran a support beam across the plane's cockpit above the AR to wire tie the adapters to. I think the arrangement of these adapters coming out of the top of the AR, the tiny vibration isolators on the AR and the quality of the adapters made the unit's battery connections susceptible to the vibrations in my plane. I have tested the returned/involved AR on the bench several hours w/o incident. The EC3 to MPX adapters were the closest thing I could find to a "smoking gun." However, seeing how they both apparently went at the same time still leaves me a bit worried, though. Got to do some more bench testing before this unit goes back in a plane. In the meantime, I have over 5 hours of stick time on the AR 9210 that I replaced it with. With the vibration mods and new adapters, it seems to be working just fine.