Flashing Yellow Light Cannot Arm

My autopilot will not arm no matter what I do. This is not a 3DR pixhawk. The pfd shows no other indication of a failure besides Disarmed. The regular arming method (left bottom corner) wont arm it. Also I cannot connect to the mavlink when I load any other firmware besides 3.4.

Hi Adam,
I have written up a detailed set of diagnostics for arming failures here:
plane.ardupilot.com/wiki/arming- … ure_to_arm
Cheers, Tridge

Thank you im sure this will help, but now im unable to load firmware on the latest version of MP. I get a Invalid Cert whenever i try to upload the firmware now. How could i go about signing my hardware?

the “invalid cert” message should only be a warning, it shouldn’t prevent you from uploading.
If it is actually preventing upload then can you please open an issue for MissionPlanner?
see github.com/diydrones/MissionPlanner/issues