This image shows the factory connection to the tail lights. If you look at your own connection the 3rd one down should be an empty gap, this is where you will need to add your own cable as I have done in blue. I didn't make a proper connector I just neatly placed a wire inside and then taped it securely it was meant to be a temporary solution but I haven't had any issues so I'll leave it like this for now.
You would have to do this on both sides, the connection to the led plate lights in on the driver side therefore the drivers side wire can be shorter and the passenger one long to reach the other side of the car. I taped the wire underneath the plastic trim on the boot.
The blue line shows where I placed the passenger wire.
I have circled a part of the boot where the cables from the rear bumper come through the firewall. It contains the parking sensor cables and importantly the led number plate lights.
I will take the boot carpet out again this weekend to show you exactly where I tapped into the plate lights. If you follow the bunch of cables back you should see a grey cable (IIRC) which should have a exposed connection I just wrapped my blue wires to this.
I apologise if the description doesn't suffice, I done this mod a few months ago.
