Check engine light and airbag warning light off/on

I have a 2008 Pontiac Wave, and recently the check engine light and the airbag warning light have been going on and off at the exact same time.

My OBD2 reader is showing a P0420 code, but the last time I checked that code was shown as a pending code. I've had trouble in the past with the P0420 code, and had the oxygen sensors tested/replaced, as well as swapping out the catalytic converter to see if that was causing the code.

I'm starting to wonder if this is a wiring issue, simply because the CEL and the airbag warning light are coming on and off at the exact same time, every time. When I dealt with the P0420 code in the past, the computer needed to complete a full drive cycle (often took a day or two) before the code would clear and the light would go off. Currently, the CEL light and the warning light come off and on seemingly at random, but sometimes within minutes - nothing close to a full drive cycle.

I looked up the wiring diagrams in Chilton's, but while I'm deciphering them - does it sound like a possible wiring issue? Has anyone had any similar problems?