"I'd make ultra-sure you've got the wire pinouts correct. You might need to use Mission Planner to gain access to the BRD_PWM_COUNT which could have possibility defaulted to something non-usable. I don't think RELAY_PIN matters, but RCx_FUNCTION…"
It turns out if you've ever clicked on "Point Camera Here" in APM Planner, it will do something like a "Do-Set-ROI" which changes the value of the parameter MNT_MODE = 2 (MavLink_targeting), with the result being that it will forever ignore…"
"I - I've performed the calibration a few times over having it set up. Camera on its back, pointing at the sky and as "level" as I can make it. After the calibration is looks like its reading zeros on pitch/tilt/roll when the camera is pointing…"