Tractor Trailer Base Frame
A basic trailer frame that is fully equipped to be used with the Modern Semi-Truck
This trailer automatically applies the brakes when the hitch is disconnected, or will lock the brakes if the air pressure drops below a certain value.
The legs (or trailer jack) work via a three stage process, the first stage being slightly raised, second stage being raised even further, and the third stage being fully retracted and folded up against the bottom of the trailer frame.
Be sure to turn off the truck before activating the hitch, to ensure the states of both trailer and truck composite signals match. (Otherwise the tail lights may de-sync and turn off when the truck is running and stay on when the truck is off)
This is a template, fully ready for you to build whatever trailer YOU want, and I look forward to seeing what you come up with :)