This is the same setup i was working on in the spring when i had all the issues with my trailer lights not being at the proper voltage. My 13 trailer is all LED and i mounted all the lights to the inside of the frame. When i tied them into the trailer harness <like you did> everything went dim and i lost my MOOMBA fender lights.

Planning on woking on this more this winter.

Also i ran Amber the rear of my fenders, then switched to Red. Looks sweet when i use a 9v battery LOL.