Color Code 7 Pin Trailer Wiring. Then all you would have to worry. Dark green is right turn, yellow is left turn.
The worst that usually happens with screwy trailer wiring is a blown fuse on the tow vehicle—or something wacky, like reversed turn signals or blinking. There should be a common color for both the tail lights. Wiring up a truck for trailer towing isn't as hard as it looks; many new trucks come prewired from the factory, and there are kits that make the operation plug and play.
This color trailer wiring diagram will help you when you need to connect your trailer to your truck's wiring harness or repair a wire that isn't working.
Dark green is right turn, yellow is left turn.
Verify the harness color codes at each tail light. Trailer Wiring Diagrams showing you the typical wiring for most single axle trailer and tandem axle trailers. Note that different color coding can be used for certain functions, which means that you can not trust the colors mentioned here without measuring the contact and wiring from case to case.