A facility exists to monitor the loaded aircrafts available power so that all Goflight hardware is turned off if the aircraft has no power available.
To setup this facility, load the aircraft you wish to use and get the flight sim into Sim Mode (at a Virtual Cockpit or 2D panel). The "Aircraft Power" button on the Status tab should now be enabled, click on this to provide configuration options.
Many aircraft use the built in battery facilities of the flight sim so by determining what battery voltage the aircraft uses, clicking the relevant "FS Default" will set everything up. To check its correct, simply drain the battery and all GoFlight equipment should turn off at the time it turns off in the flight sim. If it doesn't try the other voltage option.
Some complex airliners model their own electrical and battery systems and cannot use the FS Defaults. A way around this issue is to see if a suitable Lvar is available for battery voltage or main bus voltage. The next best option would be to see if an Lvar exists for a suitable button or switch such as the battery button and monitor its position.
The Avionics configuration options determine if the aircraft has avionics power. Configuring this and then setting appropriate GoFlight devices to AV_ENABLED instead of ENABLED will cause the GoFlight device to only activate its displays/LED's if avionics power is on. So for example if you configure GF166's for radios and set them to AV_ENABLED, they will only power up once the Avionics Power switch has been turned on in the aircraft - just like the real thing!
The FS Default buttons also configure the Avionics settings for default aircraft. This may work in complex airliners, but if it doesn't follow the advice above regarding Lvars for Power settings.