Hi this is how I sorted my lighting plug on my t6 bmotion
Brought a £30 cam bus relay took fused live feed from batt in conduit to rear remove grommet under bumper,unscrew rear light lense feed cable up through hole through grommet feed 3 core from other light up over down out of same hole through grommet bring 7 core cable ftom tow plug through same as live feed.
So now you have 7 core cable 3 core from opp side live feed from batt all hanging out of hole behind left rear light make connections to lighting wrap relay in insulation tape push relay through hole,and insulated wire connections replace crommet re fit light lense job done,I took my tow bar off T5 re fitted to t6 left previous relay on T5 so whole job cost me £30 and about 3 hrs of my time,fitted side sport bars pria so while I had plastic guards of I installed live feed in conduit before re fitting guards hope this may help someone I've done this to my last 2 transporters without issue
So it's had 4 years in service