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Trailer wiring diagram for 4, 5, 6 and 7 pin plugs
On every common trailer plug the white wire is the ground, and on a 4 pin flat plug brown runs the tail lights, yellow the left turn and brake light and green the right. Pick your connector to see each pin's function and usual wire colour from the vehicle side or the trailer side, then use the fault finder when a light stops working.
7 pin RV blade (traditional colours)
Travel trailers, fifth wheels and campers; often found on pickups and SUVs with a factory hitch.
Vehicle socket, contacts facing you, key at the top.
| Pin | Function | Usual wire colour |
|---|---|---|
| Upper left | Tail, side marker and licence plate lights | Green |
| Upper right | 12 volt battery power (charge line, accessories) | Black |
| Right | Right turn signal and brake light | Brown |
| Lower right | Electric trailer brakes (brake controller) | Blue |
| Lower left | Ground | White |
| Left | Left turn signal and brake light | Red |
| Centre | Reverse lights | Yellow |
The colours CURT lists for the traditional layout, common on fifth wheels, travel trailers and campers. The centre pin is reverse lights in this layout; some vehicles and trailers use it for another function.
Wire colours vary between makers, model years and older trailers. Before you connect or splice, confirm each pin with a circuit tester.
Trailer light fault finder
Pick the symptom you see with the trailer plugged in and the lights switched on.
Sources, checked November 6, 2026: CURT Manufacturing, Trailer Wiring Diagram and Installation Help (curtmfg.com/towing-electrical-wiring), for the 4, 5 and 6 pin and the 7 pin RV blade colours; Grote Industries, Heavy Duty 7-Way Connectors (grote.com), and Erich Jaeger, SAE J560 contact allocation (erich-jaeger.com), for the heavy truck 7 pin round; etrailer.com, Trailer Wiring Diagrams, for the surge brake use of the fifth pin and swapped 6 pin circuits. SAE J560 and SAE J2863 are the standards. The diagrams on this page are our own drawings.
Why the wiring has to match
The tow vehicle sends each light, the brake controller signal and battery power down its own pin. If one wire lands on the wrong pin, the trailer can flash the wrong turn signal or show no brake lights at all, and the driver may not see it from the cab. A poor ground causes many trailer light faults, so the white wire deserves the first check.
Catch lighting defects before the trip
Drivers record trailer light and connector defects on the High Point GPS electronic DVIR, so the shop sees them the same day. FleetZap turns each defect into a work order with a record for the trailer, and maintenance reminders by distance or engine hours keep inspections on schedule.
Get a quoteTips for trailer wiring
Test every function with the trailer plugged in before each trip: tail lights, both turn signals, brake lights and, if fitted, reverse lights and brakes.
Run a ground wire from the plug to the trailer frame: the hitch, coupler and safety chains do not make a reliable ground.
Keep the plug off the road and close the socket cover when nothing is plugged in, so water and road salt stay out of the pins.
Identify an unknown wire with a circuit tester, never by colour alone: colours vary between makers and on older trailers.
Trailer wiring questions
- What do the colours mean on a 7 pin trailer plug?
- On the common RV blade plug in the traditional colours, white is ground, green the tail lights, red the left turn and brake light, brown the right, blue the electric brakes, black 12 volt power and yellow the reverse lights. The SAE J2863 colours differ: brown tail, yellow left, green right, orange 12 volt and grey reverse.
- How do you wire a 4 pin trailer plug?
- A 4 pin flat plug has four wires: white to ground on the trailer frame, brown to the tail, side marker and licence plate lights, yellow to the left turn and brake light, and green to the right turn and brake light. Turn and brake share one bulb on each side, so a vehicle with separate bulbs needs a taillight converter.
- Is a 7 pin RV blade plug the same as a 7 pin round plug?
- No, and they do not fit each other. The RV blade plug has flat contacts and is often found on pickups and SUVs with a factory hitch. The heavy truck 7 pin round plug follows SAE J560: pin 1 white ground, 2 black markers, 3 yellow left turn, 4 red stop, 5 green right turn, 6 brown tail and 7 blue for trailer ABS power.
- Why do my trailer lights flicker or go dim?
- A poor ground is the most common cause. When the white wire has a loose or corroded connection, current looks for another path through the bulbs, so lights glow dimly, flicker, or come on together, like a turn signal that also flashes the tail lights. Clean the ground connection on the frame and in the plug, then test again.
- Which pin powers electric trailer brakes?
- On a 6 pin round plug, a 7 pin RV blade plug and a light duty 7 pin round plug, the blue wire carries the brake controller signal to the trailer brakes. A 4 or 5 pin flat plug has no brake pin. On a heavy truck SAE J560 plug, blue is constant power for the trailer ABS, because those trailers have air brakes.