Electrical plug wiring (pinout)

Trailer plug wiring diagram

pinout	example plug	pin description
		1 - Left indicator 2 - Rear fog lamp 3 - Earth (ground) 4 - Right indicator 5 - Right position (tail) light 6 - Brake lights (left and right) 7 - Left position (tail) light 8 - Reversing light 9 - Permanent +12V (battery) 10 - Switched +12V (ignition) for loads when the engine is running, e.g. caravan fridge 11 - Not assigned / free 12 - Not assigned / free 13 - Earth for pins 9 and 10

Common faults:

all lights flash / weak intensity

problem

When you switch on an indicator, several other lights flash as well, with a weaker intensity.

cause

This is due to an earth (ground) fault on that light: the return to earth passes through the other bulbs, which makes everything flash.

solution

Check that the earth (ground) connections are correctly made. Some trailers use the chassis as earth, and oxidation often forms on the screw connecting the chassis earth to the lights. Replacing the screw or the oxidised cable will solve the problem.

Problem with LED lights

see our page: LED lights compatibility

Everything works except 1 light

problem

Everything works but 1 light does not.

cause

several possible causes:

oxidised wire in the plug (car or trailer)
broken wire
blown bulb

case of the rear fog lamp

solution

Open the lens and check that the bulb is not broken (broken filament) and makes good contact. If still nothing, use a multimeter to check whether there is 12V between the bulb contacts. If there is 12V, either the bulb is broken or there is oxide on the contact tabs.

If the tabs are oxidised, scrape them to restore a clean contact.

If there is no 12V on the tabs, check the cable and the connections upstream.

If it is the rear fog lamp that does not work, it may be due to the car's socket. Indeed, some vehicles have a micro-switch that turns off the car's rear fog lamp when a trailer is connected. So check that the plug is fully inserted and that this micro-switch works correctly.