Not long after posting my question re: pin C9 the following was found in a larger wiring diagram.
13254
From this diagram the wiring to C9 is correct. I suspect now the issue is the ECM failing....

New member - assistance required with 1227747 which is installed in a 81 Jeep CJ5 with SBC350

I've been tracking down a "no starter" condition that was occurring only after driving for a period. ...