This is schematic for 2014 on Roadster showing BCU driven footwell lights. I would imagine yours would be similar as cable colours and BCU pinouts match.
![[Linked Image]](https://i.imgur.com/y2OPKbK.png)
As you will see either door switch puts a ground to BCU pin 22 which is passed on to LED lights via a timer in the BCU. I doubt there is a relay as such to switch such a low current just TTL circuitry of the timer. The permanent fused positive feed on brown/blue wire completes the circuit to the three LED strips so lights work without ignition key when a door is opened, but just for a time.
Should be an easy retro-fit.
