It would depend on what’s wrong with it. Did he say that it wanders but stays in a general direction ? Or does it not hold any course or even a general direction? If it oscillates greatly, but generally is within 20 degrees or so it could be air in the hydraulic system, Or a voltage problem with the fluxgate compass. Bringing up another point, Does it get it’s heading input from fluxgate or gps heading sensor? Could be a gps output sentence improperly formatted. Did PO mention if he replaced fluxgate or gps and it stopped working correctly. I have seen APs get confused when it gets true heading input, but CTS to waypoint in magnetic. There’s about 15 selections of ‘data’ do you have to ensure it is receiving the one correct nema sentence. So, It may not be just the AP manual you need. You have to make sure all components are up to snuff. Is there a chart plotter that uses the same heading input? Check to ensure the heading is constantly correct.
Unfortunately I have a Comnav. Apples and oranges. Even though mine is ancient, I called the left coast and they helped me out hooking up waypoint feedback to control autopilot. Maybe Wagner would as well!?
Looking up a Wagner....... that uses an internal compass with a sensor disc. If the internal magnetic compass is out of oil, or needs adjusting that would account for lack of ability to follow a heading. Or, Later installations of wiring could be slewing the compass. Turning electrical appliances on or off to see if it effects steering would be a place to look also.
