RV-6

Why does my gmc 507 ap head after about 45 seconds in use, violently pitch up? It sends the pitch trim tab full nose up every time. All the Autotrim is turned off, esc is disabled, Ray Allen pitch servo. Yesterday while testing the roll system after about 4 minutes, the AP turned on the ALT hold and then it pitched up. I just don't get it.

Sounds like a bad switch or wiring problem. Try your AP at different power settings it might show the fault at various vibration levels.