I made my 1/16 trailer with the WPL B36. together with a Bruder trailer just like yours. I didn't customize all the electronics for the trailer though, I just disassemble a cheap RC trailer and glued all its parts on the Bruder trailer. lol
The max turning shut off happened to me as well. I remember it was the servo pushes wires on max turning angle inside the cabin make on of the headlight short-circuited. I rewired the LED, and it went away for me. If yours still shuts off on the max turning angle, I suggest you take a look at all the wiring inside.