Markdun, thanks for the reply and the reason I ask: I had a similar problem with my Tecnam trim recently. After purchase I flew it from Qld, home to SA. At 065 over Dalby I handed control to my mate (also a pilot) and I switched trim control to the right yolk. After a few minutes the trim run away to a full nose down attitude. Not fun with a full flying tail plane. Done the usual, undone everything I performed earlier and got it flying again. Thought it was switches in the control column so I contacted a licensed aircraft electrician and he found the same audio plug connector in the tail corroded so he removed it. Don’t know why but the next day in my hangar I got my wife to operate the right trim while I rattled connectors and wiring that ran through the fuselage, suddenly it went into a full nose down attitude then popped the circuit. Found the problem to be chaffed loom wires deep in the fuselage, one chaffed near through, i had to use a wand camera to see the problem. (I have pics) Maybe the Tecnam you ferried has the same problem.
steve