When you say you "Checked wiring continuity ok.", unless you mean you did what I'm going to suggest, never mind, but if not, I'd suggest checking for change in resistance across the position potentiometer (pot) in the servo as the trim tab moves. Obviously measure resistance as close to the Skyview as you can to include the maximum amount of the harness in the check. If it's not changing state between the wiper and both ends of the pot, then you've likely got a bad connection between the harness and the pot connection.