13-Pin Trailer Wiring Diagram
This is a free printable 13 pin trailer wiring diagram: download the diagram as SVG or open it and print to paper or PDF.
The 13-pin trailer plug follows ISO 11446 and combines the functions of the older 7-pin N-type and S-type connectors into one — carrying all lights, reversing, fog, a continuous 12 V supply, and a switched 12 V supply for trailer refrigerators and other accessories.
The 13-pin connector (also called the Euro 13-pin) is the standard trailer coupling for cars and light commercial vehicles in Europe and many other regions. It supersedes the two separate 7-pin plugs (N-type for lights, S-type for auxiliary power) that were common before ISO 11446 was widely adopted.
ISO 11446 pin functions (numbered 1–13, viewed from the front face of the plug): - Pin 1: Left turn indicator (yellow / amber) - Pin 2: Rear fog lamp (blue) - Pin 3: Earth return for pins 1–8 (white) - Pin 4: Right turn indicator (green) - Pin 5: Right tail (rear position) lamp (brown or white) - Pin 6: Stop lamps (brake lights) (red) - Pin 7: Left tail (rear position) lamp (black or yellow) - Pin 8: Reversing lamp (pink or orange — varies by national wiring standard) - Pin 9: Permanent 12 V supply (orange — for trailer battery charging or fridge) - Pin 10: Earth return for pins 9 and 11 (white, sometimes combined with pin 3 via trailer wiring) - Pin 11: Switched 12 V supply (blue or grey — ignition-switched, for trailer refrigerator) - Pin 12: Not assigned in base standard (may be used by OEM for caravan-specific functions) - Pin 13: Earth return for pin 12 (if used)
Note that pin colour coding can vary between manufacturers and national standards (e.g. DIN 72570-compliant German vehicles may differ slightly from UK-installed towbars). Always verify colours with a multimeter at the vehicle socket before connecting new trailer wiring.
Most towbar kits include a vehicle-specific bypass relay or CAN-bus interface module that reads the car's lighting signals without introducing backfeed into the tow vehicle's ECU — essential on modern vehicles with LED lighting and body control modules.
How to wire 13 pin trailer wiring diagram
- Identify pin 1 on the plug and socket The 13-pin plug and socket both have a key or flat edge that prevents incorrect insertion. Pin 1 is marked on the body. Use a multimeter and the vehicle's ignition and lights to verify which terminal is which before connecting trailer wiring.
- Test the vehicle socket's outputs With a trailer socket tester or multimeter, turn on indicators, brake lights, and tail lights in sequence to verify the correct pin activates. Check that pin 9 shows battery voltage with ignition off, and pin 11 shows voltage only with ignition on.
- Wire the trailer's lighting circuit (pins 1–8) Connect the trailer lamp assembly wires to the appropriate pins: left indicator to 1, fog to 2, earth to 3, right indicator to 4, right tail to 5, stop to 6, left tail to 7, and reversing lamp to 8.
- Connect the trailer earth (pin 3) The single earth on pin 3 returns current for all eight lighting functions. Use a conductor of sufficient cross-section to carry the combined lamp current without excessive voltage drop — inadequate earth is the leading cause of dim or inoperative trailer lights.
- Connect auxiliary power wiring (pins 9 and 11) if required If the trailer has a fridge, battery, or other 12 V load, connect the positive to pin 9 (permanent) or pin 11 (switched) as appropriate. The return uses pin 10. Ensure the cable cross-section suits the load current and run length.
- Waterproof all connections inside the trailer plug body Use proper cable entry grommets, and ensure the plug cover snaps shut over the cable. Trailer connectors are exposed to road spray, mud, and water. Poor sealing causes corrosion that leads to intermittent lighting faults.
- Test all functions before towing Walk around the trailer with a helper operating indicators, brakes, and reversing — confirm every lamp functions on the trailer. Check that the refrigerator or auxiliary circuit energises and de-energises correctly with the ignition.
Specifications
| Standard | ISO 11446 (Europe); ECE Regulation 48 (lighting) |
|---|---|
| Number of pins | 13 |
| Supply voltage | 12 V DC (vehicle electrical system) |
| Pin 1 | Left turn indicator |
| Pin 3 | Earth return for pins 1–8 (lighting) |
| Pin 6 | Stop (brake) lamp |
| Pin 9 | Permanent 12 V supply (battery charge / fridge) |
| Pin 11 | Ignition-switched 12 V supply (fridge / accessories) |
Safety warnings
- Incorrect trailer wiring is a road safety hazard. Non-functional brake lights or indicators put your life and other road users at risk. Test every function before every trip.
- On vehicles with CAN-bus lighting systems, direct connection to lamp holders without a proper bypass relay or interface module can generate fault codes, cause ECU errors, and damage the body control module.
- Never exceed the fuse ratings designed for each pin circuit — the auxiliary power pins (9 and 11) supply significant current and their wiring must be correctly sized and protected.
- Trailer wiring installations must comply with ECE Regulation 48 (lighting) and any national road traffic regulations regarding trailer equipment. Incorrect lighting renders the trailer unroadworthy.
- This diagram is illustrative and reference-only. Verify pin assignments against the specific vehicle and trailer wiring diagrams applicable to your combination.
Tools needed
- 13-pin socket tester or trailer board tester
- Digital multimeter
- Wire strippers and crimping tool
- Heat-shrink tubing or electrical tape
- Cable ties and edge grommets
- Small flathead screwdriver (for plug terminal screws)
Common mistakes
- Connecting the earth (pin 3) to only one lamp rather than providing a clean return for all trailer lamps — causes dim or non-functioning lights when multiple lamps are on.
- Confusing the permanent 12 V (pin 9) with the switched supply (pin 11), resulting in the trailer battery never charging or the fridge running when the ignition is off and flattening the car battery.
- Omitting a CAN-bus interface module on modern vehicles, triggering false bulb-out warnings or ECU faults.
- Using under-rated cable for the auxiliary 12 V circuit, causing voltage drop that starves the trailer's battery charger or refrigerator.
- Not weatherproofing the plug body, leading to corrosion inside the connector that causes intermittent or total lighting failure.
Troubleshooting
- Trailer lights dim or flicker
- Cause: High resistance in the earth connection (pin 3) or corroded plug/socket contacts. Fix: Measure voltage drop on the earth connection between the trailer lamp body and the socket pin 3 under load — should be below 0.5 V. Clean or replace corroded contacts. Ensure the trailer earth is bonded directly to the trailer chassis.
- One indicator on the car flashes at double speed (hyper-flash)
- Cause: The corresponding trailer indicator lamp is not working, and the car's indicator relay detects reduced current load. Fix: Check the trailer indicator bulb and its wiring. If LEDs are fitted, a load resistor or CAN-bus relay module may be needed to simulate the expected incandescent bulb resistance for the car's flasher relay.
- Car battery drains overnight with trailer connected
- Cause: The trailer has a load on pin 9 (permanent supply) that is drawing current continuously — typically a fridge or a battery charger left connected. Fix: Disconnect the trailer when parked unless shore power is available to maintain the car battery. Consider fitting a battery-to-battery charger with automatic isolation to prevent discharge below a threshold voltage.
Frequently asked questions
What is the difference between the 13-pin connector and the old 7-pin N and S type plugs?
The 7-pin N-type (ISO 1724) carried the seven lighting functions. The 7-pin S-type (ISO 3731) carried two 12 V power supplies and a separate earth. The 13-pin ISO 11446 connector combines all of these into a single waterproof plug, simplifying connection and reducing coupling time.
Which pin supplies power to a caravan refrigerator?
Pin 11 provides a switched (ignition-on) 12 V supply typically used for a caravan refrigerator while travelling. Pin 9 provides a permanent (always-on) 12 V supply for battery charging. Both have their own earth return on pin 10. Check your caravan's wiring diagram to confirm which pin your fridge circuit uses.
Why do I need a CAN-bus relay module for my towbar?
Modern vehicles control lighting through a body control module (BCM) that monitors current draw and detects bulb failures electronically. Directly adding a trailer to the bulb holder wiring confuses the BCM, triggering false fault codes. A CAN-bus module reads the signals at the right point and drives the trailer lights independently, preventing these issues.
What fuse ratings are used for the 13-pin circuit?
The lighting circuit (pins 1–8) is typically fused at 7.5 A or 10 A. The permanent 12 V supply (pin 9) is commonly fused at 15 A. The switched supply (pin 11) is typically fused at 10–15 A. Fuse ratings depend on the vehicle manufacturer's design — always follow the vehicle wiring diagram.
Can I connect a 7-pin plug trailer to a 13-pin vehicle socket?
Yes, using a purpose-made 7-to-13-pin adapter lead. The adapter maps the 7 lighting functions across to the appropriate 13-pin terminals. The 12 V power pins (9, 11) are not used if the trailer has no auxiliary power requirements. Never improvise adapters by cutting and rejoining connectors.
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