I have a 2014 trailhawk (LEDs).
I cut and installed two relays for the brake/turn, and diodes for the tail.
You can't drill the housing for adding bulbs.the relays are switched by plugging in the 7 pin trailer light cable. Basically the relays switch the lights from car t o coach control.
Do I g it this way let's my brake light flash when turning AND braking at the same time.
2014 40QBH Phaeton DP Cummins 380HP ISL, Freightliner XC, 2019 Jeep Grand Cherokee Trailhawk TOAD
Blue Ox Aventa tow bar, SMI Air Force One -Cave Creek, AZ.