AV Cable (Xbox Original)

The Xbox Original can have sevaral types of cable (composite or component), has digital and analog audio, and mode select pins to detect which cable is inserted.

The SMC handles detecting these cables by the cable grounding one of several mode pins.

Image of AV cable pinout thanks to https://gamesx.com/avpinouts/xbox.htm

If you do not have a cable present, you can just ground pin 19 for example to set the cable detection into outputting NTSC Mono and bypassing the orange flashing light.