This guide is not meant to be a full training manual on all aspects of RV wiring, rather it is designed to help the average do-it-yourselfer find and repair the most common wiring problems. If you are not comfortable using tools or if the problem is found to be in the wiring harness of the tow vehicle, it is recommended that you seek the help of a professional.
Most problems with RV wiring originates in the tow vehicle socket and/or the trailer plug. With all the rain water, road salt, and grime thrown up by the tires, these components are subjected to the worst conditions for an electrical connection.
First, check the inside connections of the tow vehicle socket for corrosion, broken wires or other obvious problems.
Then inspect the trailer plug for the same conditions. Any deterioration of the terminals or the wires themselves should be repaired now. It is often more economical (and less stressful) to replace the entire plug/socket and make any needed repairs to the wires at this point. Often the problem is solved before delving deeper into the wiring maze.
It's not as hard as you think!
Wiring the 4 pole utility trailer plug
Wiring the 6 pole horse trailer plug
Wiring the 7 pole RV Tow Vehicle Socket
| Terminal | Wire Color | Function | Location - Truck | Location Trailer |
| 1 | White | Ground | uncovered pin | covered pin |
| 2 | Brown | Running Lights | 1st covered pin | 1st uncovered pin |
| 3 | Yellow | Left turn/brake light | 2nd covered pin | 2nd uncovered pin |
| 4 | Green | Right turn/brake light | 3rd covered pin | 3rd uncovered pin |
| Terminal Marking | Wire Color | Function |
| GD | White | Ground |
| TM | Brown | Running Lights |
| LT | Yellow | Left turn/brake light |
| RT | Green | Right turn/brake light |
| ST | Blue | Brake Control |
| Aux | Black | Power |
| Terminal Marking | Wire Color | Function |
| GD | White | Ground |
| TM | Green | Running Lights |
| LT | Red | Left turn/brake light |
| RT | Brown | Right turn/brake light |
| ST | Blue | Brake Control |
| Aux | Black | Power |
There are two wiring codes for different 7 pole plug sets.
Most RV's use the RV wiring code for the type of plug/socket
that has 6 flat contacts surrounding the center round pin.
Semi's and other commercial trailers use the ASME
(American Society of Mechanical Engineers) type of 7-pole plug set.
This plug has 6 round contacts surrounding the center pin.
The wiring color code for this plug is not the same as the
RV 7 pole plug described below, and will be included at a future time.
| Terminal | Wire Color | Function | Location - Truck socket | Location Trailer plug |
| 1 | White | Ground | 7:00 o'clock | 5:00 o'clock |
| 2 | Blue | Brakes | 5:00 o'clock | 7:00 o'clock |
| 3 | Green | Running | 10:00 o'clock | 2:00 o'clock |
| 4 | Black | Power | 2:00 o'clock | 10:00 o'clock |
| 5 | Red | LT & Stop | 9:00 o'clock | 3:00 o'clock |
| 6 | Brown | RT & Stop | 3:00 o'clock | 9:00 o'clock |
| 7 | Yellow | Aux or BU | Center | Center |
Note: a "toad" is a small vehicle towed behind a motorhome.
Instead of hooking in to the cars existing system you can simply mount a very nice set of lights under the rear bumper, below the existing light array, and run separate wires under the toad chassis.
This method would eliminate the neccessity of installing diodes into the toad lighting circuits to prevent feedback problems. A four pole connector at the front of the toad connects the add-on lights to the motor homes circuits.