Upgrade of Multiplex Cockpit SX to FrSky V8FT 2.4 GHz
I have decided to mount external F/S button and LEDs.
You have to do two things. Shutdown the MHz band an bring power and PPT to FrSky. The MHz band is shut down when you bring GND to 5th pin (from left to right) near the DIN connector. When you do that, the transmitter starts up in DSC mode. This way you do not loose PPM signal that will be used by the FrSky. Now you have to bring PPM and Vdd (+) to the FrSky module. You can do that directly, as I have done in my current design, or with the bipolar switch, which connects MHz band pin to GND and simultaneously powers the FrSky module.
Everything else is only for extending signalling (LEDs) and input button, so that they can be more appropriately mounted to the unit. You can buy LEDs and button in your electronics shop.
Steps are shown in pictures...