Trailer plugs and sockets for UK and European fleets
Trailer electrical connections have standardised around two main connector types for road lighting: the 7-pin N-type (ISO 1724) for basic lighting circuits, and the 7-pin S-type (ISO 3732) for reversing lamps and battery charging circuits. Most UK and European trailers use both connectors, with the N-type carrying the seven standard lighting functions and the S-type handling the supplementary circuits.
For modern trailers with EBS, CAN bus, and telematics, the 15-pin ISO 11992 connector carries the data signals alongside the power supply. This connector type is required on any trailer fitted with an electronic braking system, tyre pressure monitoring, or remote diagnostic capability. The 15-pin connector is not interchangeable with the 7-pin connectors, and vehicles towing trailers with EBS must have the corresponding 15-pin socket on the tractor unit.
Plug and socket condition should be checked as part of any trailer inspection. Corroded pins, damaged locking rings, and cracked housings cause intermittent lighting faults that are difficult to trace and are a common cause of roadside DVSA prohibitions. Replacement plugs and sockets are inexpensive, and keeping spares on fleet vehicles is standard practice. Call us on 01527 598 000 or order online for next-day delivery.
Frequently Asked Questions
What is the difference between a 7-pin N-type and S-type trailer connector?
The N-type (ISO 1724) is the standard 7-pin connector used for road lighting circuits on trailers: side markers, brake lights, indicators, and rear lights. The S-type (ISO 3732) is a second 7-pin connector used for supplementary circuits including reversing lamps, battery charging, and fog lights. Most European trailers have both connectors. The two types look similar but are not interchangeable.
What is the 15-pin trailer connector used for?
The 15-pin ISO 11992 connector carries both power and data signals between the tractor unit and trailer. It is required for trailers fitted with EBS (Electronic Braking Systems), CAN bus communications, tyre pressure monitoring, and remote diagnostic systems. Any trailer with electronic braking must have a 15-pin connection to the tractor unit.
How do I know if my trailer plug needs replacing?
Inspect the plug and socket at each hitching. Signs that require replacement include corroded or missing pin contacts, a cracked or broken housing, a damaged locking ring that no longer secures the connection, or intermittent lighting faults that clear when the plug is wiggled. A visual inspection takes seconds and avoids a roadside prohibition for a lighting fault.
Can I repair a damaged trailer plug rather than replace it?
Minor corrosion on pin contacts can sometimes be cleaned with electrical contact cleaner. A cracked housing, a bent pin, or a broken locking mechanism requires replacement. Trailer plugs are relatively inexpensive: the cost of replacement is significantly less than the time spent diagnosing an intermittent fault caused by a poor connection.
