I couldn't edit the last post (3600 second limit...)
I started the plane, turned the Fuel Pump on, watched the status of the variable 'A:CIRCUIT CONNECTION ON:4' in Data Monitor, and tripped the breaker. That A-Var is a standard Simconnect variable, so I should see it changing. There was no change.
Tripping the breaker shut the pump off, so I know it's interrupting the circuit.
I need to be able to monitor the breaker status, and can't see how.