[Fun-Lovin]

I ran into similar problems when working with my dads a/s.
When testing everything on the trailer worked, but when I hooked to his truck directly nothing worked. His problem turned out to be the plug on the trailer and the cable to the truck didn't want to work together well. It was just sure age and use of the original socket and plug. I replaced both with the new rv style 7 round plug and socket and it all worked perfectly.
Normally the brake and turn lights are the same, the tail lights are combined on both sides.
Here is a suggestion for you to run down and find out exactly what you have and what pins go to what lights. Use a circuit tester (its a light in a probe with a wire and a gator clamp). Use this to find the correct wire on the tow vehicle if you don't already know what they are. Clamp the gator clip to a good ground on the tow vehicle, test each circuit (l,r turns and tail lights, power wire). Once you know and label these your ready to get started. I built a set of jumper wires to test the trailer lights using 16 guage wire and gator clips. Clip one wire to a good ground on both tow vehicle and trailer, connect power wire on tow vehicle to other jumper clip (you may want a fuse in this wire but not a big one 5 amps) one at a time check the wires to the trailer wiring harness. this will tell you what connection on the trailer goes to what. This is trial and error but works. If you blow the fuse you may have hit the ground.