US built trucks have the same color codes , brown, tail marker, green, right turn, yellow left turn. white, ground . Ground your trailer to the truck useing a ground right off the trailer frame to the plug then right to your truck frame. Your turn signals will work as long as the brake lights come, interupter switch in the truck.
Most all problems with trailer lights is the GROUND. check the connection in the plug, even a little dirt or rust will weaken your power, you may have solid ground frame to frame but the pluc might be the culprit.
A Dumb Ass is someone that tries something, that will not work, change nothing, and expect differnt results.