One possibility is that the adaptor harness is bad, also check to see that the plug from the Y harness to the airtronics adaptor is not plugged in backwards, yes universal style plugs will go in 180dg out surprisingly easily in many cases, their keying is not all that positive.
I too have all old style Airtroncs RX that I use them with a mix of new and old servos, all my new universal style servos, ESCs and switch harnesses have the pos and neg wires reversed and they are plugged directly into the Rx, been doing it for some years and I haven't smoked one YET
(I sooo will regret saying that.) I mention this way of dealing with the issue while it has risks while hooking up a system, it does result in greater reliability by eliminating extra connectors. Good luck.
Pete