You can find almost all of the hardware inputs in the "Hardware Inputs & Outputs" section of the manual. For the autopilot, you will find the standard native bindings under the "Instrument Events" heading:
K:AP_PANEL_HEADING_HOLD
K:AP_NAV1_HOLD
K:AP_APR_HOLD
K:AP_BC_HOLD
K:AP_ALT_HOLD