In the manual the S-TEC 55 autopilot will be powered ON by setting master- and stabilisator-switches ON.
But doing so, the screen of the autopilot remains blank. No annunciator lights for 5 seconds, no RDY annunciator.
I'm unable to reproduce the issue in FSX:SE and P3D v4. From a cold & dark configuration, switching on the master and then pushing in the stabilisator switch breaker turns on the autopilot correctly.
Can you submit a support ticket so we can investigate further?
I am having the same problem. When I hover the mouse over the stabilator switch it will not activate. I have tried deleting and reinstalling the plane with no help. I need som suggestions please.