The spoiler brakelight wiring is on the right side along with the trunk lock control wiring.There are 12 wires there. Three of the colored wires and one *********** the two rear speakers, the other two colored ones power the heated backrest. The other 3 white, and all 3 black go to an unused connector, however maybe that is your 3rd brake light. I don't have a 3rd brake light.
Reconnect the matching colored wires and then turn on the radio and try each white wire combination until you get sound from your right rear speaker.Found these wires cut (6) in the left side wire hardness in the trunk, they run up into the trunk cover. My third brake light still works, not clear what these wires control and do I need to splice them back together?