Get the manual. Follow the rigging checklist. Perform the flight test.
But before that beautiful two-axis (or three-axis) system keeps your wings level on an IFR cross-country, there is one document that stands between you and success: . S-tec 55x Installation Manual
The 55X is a rate-based, roll-stabilization system. That means it relies heavily on the turn coordinator and the specific rigging of your servos. If you skip steps in the manual, you end up with a wandering heading bug or, worse, an autopilot that oscillates (the dreaded "S-TEC wobble"). While the specific page numbers vary by revision, a legitimate installation manual covers four critical areas: Get the manual
The 55X is a phenomenal autopilot—it holds altitude like a glider and tracks GPS courses tighter than most modern digital units. But it is an analog soul in a digital world. It demands respect for torque curves, slip rings, and precise voltage. But before that beautiful two-axis (or three-axis) system
Your back will thank you when you are sipping coffee, hands-free, at FL180.
The manual provides the exact schematics for the 55X Computer (PN 01194-0-1 or similar). You will find the pin assignments for the Roll channel, Pitch channel (if installed), the altitude hold, and the connection to your GPS (Garmin, Avidyne, or Aspen). Connecting the wrong pin to the serial encoder is a recipe for a smoked circuit board.