Trailer Wiring Diagrams | etrailer Trailer Wiring Diagrams. a reverse lockout on trailers with surge brakes. When this is the case, the lockout should be connected to the backup light circuit of the tow vehicle. 4-Way such as the larger 7-way round plug, you can use our adapter fitguide to find the one that is right for your vehicle and trailer. Troubleshoot Your Trailer 7 Way Plug Wiring Diagram - Country Trailer Sales PDF file7 Way Plug Wiring Diagram Standard Wiring* Post Purpose Wire Color TM Park Light Green (+) Battery Feed Black RT Right Turn/Brake Light Brown LT Left Turn/Brake Light Red S Trailer Electric Brakes Blue GD Ground White A Accessory Yellow This is the most common (Standard) wiring scheme for RV Plugs and the one used by major auto manufacturers today. How To Test 7 Way Trailer RV electrical Plug - YouTube Click to view on Bing4:30How To Test 7 Way Trailer RV electrical Plug In this video I show how to test a 7 way trailer plug wiring harness for towing a travel trailer or RV by using a led trailer light adapter tester to test signals, brakes and running lights Author: LittleRVrentalsViews: 181K