If I’m right with my purpose the purple wire must also gives a 12V Signal when you power the transmitter with 12V.
If so you have to use a transistor (a BC457 or BC458 can do the job) and wire it like this:
- purpel wire to a 33KOhm resistor, the 33Ohm restistor to the base of the transmitter.
- also from the Base a 100KOhm resistor to ground
- the emiter goes to TX or RX on the transmitter
- and on the colector you wire a 1k5Ohm resistor
- at the 1K5Ohm tesistor you wire the +12V
But if you do this be sure that the transmitter can handle 12V on TX/RX.
Its similar to this the only change is that the emiter don’t go to ground but tu TX or RX.