Hello,
you can connect secondary satellite to the RUD port only.
Throttle must be connected to the AUX.
If you will use Y-harness, you can connect battery to the RUD (second free Y-harness cable).
In this way, it will work without any problem.
If you will need second power input, you can also use second Y-harness in the AUX.
If you are using classic receiver connection, then there are two power leads so you are feeding the unit from receiver.
How to power the red fbl system
Spirit System developer