Trailer Wiring Diagram

Not sure which wires attach to what on your trailer connectors? Does one of your turn signals not work and you’re not sure which wire to inspect? Check out or trailer wiring diagrams for a quick reference on trailer wiring. The below information is for reference and is commonly used throughout the industry, but can vary depending on who built the trailer. You can use a circuit tester to verify connections.

Trailer Connectors

Trailer electrical connectors come in a variety of shapes and sizes. The basic purpose remains the same whether your truck and trailer is using a 4-way, 5-way, 6-way or 7-way connector. By law, trailer lighting must be connected into the tow vehicle's wiring system to provide trailer running lights, turn signals and brake lights. This is accomplished by tapping into the tow vehicle's electrical harness to transfer power to the trailer wiring system. Trailer connectors are used between the two to allow disengagement when not towing.

Various styles of connectors are available with four to seven pins to allow transfer of power for the lighting as well as auxiliary functions such as electric trailer brake control, backup lights etc. The trailer wiring diagrams listed below, should help identify any wiring issues you may have with your trailer. When shopping for trailer connectors remember that the male end is mounted on the vehicle side and the female on the trailer side.

4-Way Trailer Wiring

4-Way trailer connectors are typically used on small trailers such as boat, snowmobile, utility and other trailers that that do not use brakes. As the name implies, they use four wires to carry out the vital lighting functions. The four wires control the turn signals, brake lights and taillights or running lights. They also provide a wire for a ground connection. 4-way trailer connectors are available in two styles: flat and round. They have the same electrical functions, but they do have a few differences.

4-Way Round Pin Connector

The image below shows the connector from the back side, where the 4-wires are attached with screws. 4-way round connectors are commonly sold without the wires, although complete kits are available. Typically made from die-cast metal construction, they offer a concealed terminal with a dust cover for protection against the elements.

TRAILER END

CAR END

tow vehicle end - 4 way round pin connector

4 & 5 Way Flat Connector Wiring Diagrams

4-way and 5-way flat connectors use color-coded wires and are available in a variety of lengths. They can be purchased as a standalone plug for the truck or trailer, or as a complete loop with both the plug and the socket included. They often use bonded wires for a reliable connection and have rubber construction to protect against the elements. The wiring is very similar, the only difference is the 5-way will have an extra blue auxiliary wire that is often used for backup lights.

4-Way Flat Connectors

5-Way Flat Connectors

TRAILER WIRING

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6-Way Trailer Connectors

6-Way trailer connectors are often used on gooseneck trailers, but can be used for other types such as utility, boat trailers and 5th wheels. 6 way connectors include the basic connection of running lights, brake lights, turn signals and a ground wire. They also have one wire for trailer brakes and one wire for a battery connection. These additional wires allow a for trailer brake controller to be installed and a connection between the vehicle's power supply and a 12-volt battery for a breakaway kit or an additional auxiliary power source.

6-Way Molded Trailer/Sealed Car Connector & Cable

Trailer End

As viewed from front face of 6 way connector with molded on cable.

Car End

As viewed from front face of 6 way connector with molded on cable.

6-Way Zinc Die-Cast Connector

Trailer End

As viewed from core back side where wires are attached with screws.

Car End

As viewed from core back side where wires are attached with screws.

6 - Way Wiring Index

Wire Color & Gauge	Molded Trailer/Sealed Car Connector Terminal	Zinc Die Cast Connector Terminal
White / 10/14 Gauge	Common Ground	GD - Common Ground
Blue / 10/14 Gauge	Electric Brake	S - Electric Brake
Green / 14 Gauge	Right Stop & Turn	TM - Tail & License
Red / 10/14 Gauge	Auxiliary	LT - Left Stop & Turn
Brown / 14 Gauge	Tail & License	RT - Right Stop & Turn
Yellow / 14 Gauge	Left Stop & Turn	A - Auxiliary

7-Way Trailer Connectors - Blade Style

7-Way trailer connectors are found on most recreational vehicles and are used on larger gooseneck, 5th wheel, boat and utility trailers. They supply power to the taillights, turn signals, brake lights, trailer brakes, reverse lights, auxiliary power and include a ground connection. They come in two variations, 7-Way round and 7-way with RV Blades. They look similar, but it is important to verify which one you have before replacing it. The blade style is very common and will have small blades that are used for the connection. The round style has small round pins that are used to connect the two.

7-Way Molded Trailer/Sealed Car Connector & Cable

Trailer End

As viewed from front face of 7 way connector with molded on cable.

Car End

As viewed from front face of 7 way connector with molded on cable.

7-Way Thermo Plastic/Metal Connector

Trailer End

As viewed from core back side where wires are attached with screws.

Car End

As viewed from core back side where wires are attached with screws.

7 - Way Wiring Index

Wire Color & Gauge	Molded Trailer/Sealed Car Connector Terminal	Thermo-Plastic/Metal Connector Terminal
White / 10 Gauge	Common Ground	#1 Common Ground
Blue / 12 Gauge	Electric Brake	#2 Electric Brake
Green / 14 Gauge	Tail & License	#3 Tail & License
Black / 10 Gauge	Battery Charge	#4 Battery Charge
Red / 14 Gauge	Left Stop & Turn	#5 Stop & Turn
Brown / 14 Gauge	Right Stop & Turn	#6 Right Stop & Turn
Yellow / 14 Gauge	Center Auxiliary	#7 Center Auxiliary

7-Way Molded Trailer Connectors

Pin Clocking

Cold Weather RV - Gauge 2/10, 1/12, 4/14

Trailer End - As viewed from front face of 7-way connector with molded on cable.

Wire Color, Gauge & Function
White / 10 Gauge / Common Ground
Blue / 12 Gauge / Electric Brake
Green / 14 Gauge? Tail License
Black / 10 Gauge / Battery Charge
Red / 14 Gauge / Left Stop Turn
Brown / 14 Gauge / Right Stop & Turn
Yellow / 14 Gauge / Center Auxiliary

Heavy Duty Trailer - Gauge 2/10, 1/12, 4/14

Trailer End - As viewed from front face of 7-way connector with molded on cable.

Wire Color & Gauge
White / 10 Gauge
Blue / 12 Gauge
Green / 14 Gauge
Black / 10 Gauge
Red / 14 Gauge
Brown / 14 Gauge
Yellow / 14 Gauge

Cold Weather - Gauge 3/10, 4/14

Trailer End - As viewed from front face of 7-way connector with molded on cable.

Wire Color & Gauge
White / 10 Gauge
Blue / 14 Gauge
Green / 14 Gauge
Black / 10 Gauge
Red / 10 Gauge
Brown / 14 Gauge
Yellow / 14 Gauge

Below is an image of a trailer wiring diamgram that is very helpful to reference. Be sure to check out our trailer tips on how to wire a trailer and troubleshooting trailer lights.