[exigegus]

Per the wiring diagrams, the dual green/purple is the wire that heads out to the brake lights
Their instructions are contradictory, pretty sure it needs to be the gn/pu, the other one is power all the time when the ignition is on

 

[exigegus]

I have a vested interest in this, I have one of these kits in a box waiting for me to get a round tuit

 

[exigegus]

Hmmm

It is possible that the LED does not provide the 'ground' that is required by the circuit.
You literally have to get 12 volts or your brake lights won't work.
But an LED won't necessarily show as ground when off, and a digital circuit might need to see both 'high' and 'low'

Inserting a fairly high value resistor[say a 1k ohm] between the gn/pu wire and ground [essentially across the brake light bulb]might satisfy the need for ground without affecting the operation of the lights. It is possible it is only needed for setup although I am not sure.

 

[exigegus]

This does give a course of questioning for their tech support, IOW function with LED brake lights

 

[exigegus]

Yes one would think, but aftermarket lights might be different