How to replace a 7-pin trailer plug
A 30-minute walkthrough for replacing a 7-pin trailer plug: stripping the cable, matching wire colors to terminals, and testing every circuit before you tow.
Replacing a 7-pin RV-style trailer plug is a 30-minute job with wire strippers, cable cutters and two screwdrivers. Wire colour to terminal position is the only thing you have to get right. Get it wrong and the brake lights flash with the turn signal, or the brake controller pulls power through the wrong pin.
The standard 7-blade RV plug wiring uses this colour code on most manufactured trailers:
| Pin | Function | Wire colour |
|---|---|---|
| GD | Ground | White |
| TM | Tail/running | Brown |
| LT | Left turn/brake | Yellow |
| RT | Right turn/brake | Green |
| S | Electric brakes | Blue |
| BAT | 12V auxiliary | Black |
| A | Auxiliary | Purple or light blue |
If your trailer doesn’t match this colour code (most often the case on older trailers or DIY builds), check continuity with a meter from each pin to the corresponding circuit on the trailer before you commit to the wiring.
Tools
- Wire strippers
- Cable cutters
- Phillips screwdriver
- Flathead screwdriver
- 7-pin trailer plug (Pollak, Hopkins, etc.)
- Heat shrink or electrical tape
Steps
1. Cut the old plug
With cable cutters, cut the wire flush at the base of the old plug. You’ll lose maybe an inch of cable. You’ll get most of it back when you strip the new sheathing.
2. Strip the outer sheath
Slice the outer rubber sheath gently for about 1 inch back from the cut end. Use the wire stripper’s blade or a utility knife very carefully so you don’t nick the individual wires inside. Peel the sheath off.
3. Strip each conductor
Strip about half an inch of insulation off each of the seven wires. Twist the exposed strands tight so they go cleanly under the terminal screws without splaying.
4. Feed the cable into the new plug
Slide the cable through the strain-relief end of the new plug housing. Open up the plug to expose the seven terminal screws inside. Loosen each one a turn or two with a flathead.
5. Wire each terminal
Each terminal inside the plug is marked with a letter or the wire colour the manufacturer expects. Match each wire to its terminal:
- White to GD
- Brown to TM
- Yellow to LT
- Green to RT
- Blue to S
- Black to BAT
- Purple to A
Push the stripped wire end into the terminal and tighten the screw. Don’t over-torque. Brass terminals strip easily if you crank on them.
6. Pull the housing closed
Once all seven wires are seated and screws tight, pull the housing back over the terminal block. The strain relief at the cable end should grip the cable, not the wires. Tighten the two clamping screws.
7. Test every circuit
Plug into the truck. With a helper at the back:
- Headlights on: trailer running lights and licence plate light should be on.
- Left turn signal: left tail light should flash.
- Right turn signal: right tail light should flash.
- Brake pedal pressed: both brake lights should illuminate.
- Brake controller manual lever: trailer electric brakes should engage (you’ll feel them lock if the trailer is up on jack stands, or you’ll see the controller’s amperage display jump).
- Multimeter on BAT to GD: should read 12V if the truck circuit is wired to ignition or always-hot.
If a circuit doesn’t behave, check the terminal screw on that pin first, then the corresponding wire at the trailer end.
Quick troubleshooting
| Symptom | Likely cause |
|---|---|
| Brake lights flash with turn signal | Yellow/green swapped or shorted |
| No running lights but turn signals work | Brown wire loose or pin GD ground issue |
| No electric brakes | Blue wire loose, brake controller not powered, or brake battery dead |
| All lights dim, flicker | Bad ground (white wire) on plug or trailer |
| Auxiliary circuit dead | Black wire loose, blown 30A inline fuse |
A note on Ford trucks in 2026
If you’re plugging into a 2021 to 2026 F-150, 2022 to 2026 Super Duty, 2022 to 2026 Maverick or Expedition, or a 2024 to 2026 Ranger, recall 26C10 (NHTSA 26V104000) covers an Integrated Trailer Module software fault that can affect trailer brake and lighting signals from the truck side. Ford pushed the OTA fix in March 2026. If your trailer plug looks wired right but the truck’s outputs are flaky, check whether the recall has been completed on your VIN at ford.com/support/recalls.