A quick reference for the wire colours on a standard 7-pin flat trailer plug, what each one does, and the one difference to know if you’re wiring a European-built trailer (Variant or Scanvogn) to an Australian tow vehicle. If you’re chasing a specific fault — brake lights not working, indicators crossed, or reverse light not triggering — the colour code below is the starting point.
7-pin flat plug wire colours and what they do
| Wire colour | Function |
|---|---|
| Brown | Tail lamps and side-marker lamps |
| Yellow | Left turn signal and brake light |
| Green | Right turn signal and brake light |
| White | Earth / ground |
| Blue | Electric brakes on an Australian-wired trailer. On a European-built trailer (Variant/Scanvogn), blue is the fog light instead — see the note below. |
| Grey or pink | Reverse light. When a European-wired trailer is connected to an Australian vehicle, this wire is run to auxiliary and used for the reverse light. |
| Black | Auxiliary or permanent power feed |
European trailer wiring vs Australian trailer wiring
Trailer wiring colour codes vary by manufacturer, and this matters directly if you’re towing a European-built trailer in Australia. On an Australian-wired trailer, blue is commonly the electric brake wire. On a European trailer, blue is the fog light circuit instead — Australia hasn’t standardised fog-light wiring on trailers, so the practical fix is to run the blue wire to the service brake connection (position 5) if the trailer is on electric brakes, matching it to your tow vehicle’s wiring. This only applies to electric-braked trailers; if the trailer runs mechanical (override) brakes, the vehicle-side electric brake wiring isn’t used at all.
Every Variant and Scanvogn trailer A2B sells is under 3,500kg ATM, so no special licence is needed to tow one on a standard car licence — see our trailer buying & compliance guide for ATM, tare and payload basics.
Wiring pin-by-pin for both a 7-pin and 12-pin plug, on both Australian and European wiring — including exact pin numbers — is covered in more depth in our detailed blue-wire wiring guide.
Electric brakes vs mechanical brakes
The blue wire only carries a signal if your trailer has electric brakes and your tow vehicle has a compatible brake controller fitted. For the full difference between electric and mechanical (override) trailer brake systems, see our electric vs mechanical trailer brakes guide.
Frequently asked questions
What does the blue wire do on a trailer plug?
On an Australian-wired trailer, blue is normally the electric brake wire. On a European-built trailer such as a Variant or Scanvogn, blue is the fog light circuit instead — see the European vs Australian wiring section above for how this is handled on an electric-braked trailer.
What is the standard trailer plug wiring colour code?
On a standard 7-pin flat plug: brown for tail and side-marker lamps, yellow for the left indicator and brake light, green for the right indicator and brake light, white for earth, blue for electric brakes (or fog light on a European trailer), grey or pink for reverse, and black for auxiliary or permanent power.
Why won’t my trailer’s indicators or brake lights work after connecting the plug?
The most common cause is a mismatched colour code between the tow vehicle and trailer — this is especially common wiring a European-built trailer to an Australian vehicle, since the blue wire means something different on each (see above). Check each wire against the colour table before assuming a globe or connector fault.
Does a trailer with electric brakes need special wiring?
Yes — electric brakes need a compatible brake controller fitted to the tow vehicle and a working connection on the blue wire (on Australian-wired trailers) through to the plug. Mechanical (override) braked trailers don’t use this wire for braking at all. See our electric vs mechanical brakes guide for the full comparison.
Do I need a special licence to tow a trailer with this wiring?
No — every Variant and Scanvogn trailer A2B sells is under 3,500kg ATM, which is towable on a standard car driving licence. See our trailer buying & compliance guide for the full ATM, tare and payload rules.
Need a hand in person? Call A2B Trailers on (02) 4367 0026 or get a quote and we’ll help you sort it.
