Re: 04 GC back flipper glass
Welcome to the garage.
You will need to measure voltage on the release solenoid. If voltage is there, then the solenoid must be shot. But the voltage signal comes via an, internal to the liftgate powerlock motor, limit switch. Can be that this switch is not working anymore, preventing the voltage to reach the flipper glass solenoid.
Attached the wiring schematic for your reference.