From the tester's manual -
4.10 Trailer electric socket
You must only inspect the trailer electrical socket on vehicles fitted with a towing coupling.
If there’s no tow ball or pin, but the attachment brackets are still in place, you must assess the electrical sockets if the tow ball or pin has been:
- detached
- unbolted
- otherwise removed
You do not need to assess the electrical sockets if the attachment brackets have been deliberately made unfit for further use.
You do not need to assess the trailer electrical socket if you need tools or specialist equipment to remove access panels in the bumper or bodywork to gain access to the socket.
A trailer electrical socket with a defective or missing cover flap that incorporates a lug and spring to hold the plug in place is not considered to be a defect.
13 pin Euro-socket
On vehicles fitted with a trailer 13 pin Euro-socket, use an approved device to check that the socket is wired to correctly operate the trailer:
- position lamps
- stop lamps
- direction indicators
Some 13-pin test tools may continually flicker when plugged into the socket of a vehicle that uses controller area network bus (CANbus) systems.
Where this happens, it generally indicates that there’s continuity at each pin on the vehicle’s socket. When the lamps are operated in turn you will usually see that each individual LED will function correctly.
Provided the self-test facility on your tester does not show any faults, then you should pass the socket test.
| Defect | Category |
|---|
(a) A trailer electrical socket:
(i) insecure
(ii) likely to become detached |
Minor
Major |
(b) Trailer electrical socket wiring:
(i) insulation damaged or deteriorated
(ii) insulation damaged or deteriorated and likely to cause a short-circuit |
Minor
Major |
(c) A 13-pin trailer socket:
(i) not functioning correctly
(ii) not functioning at all |
Major
Dangerous |
Inspection processes and rules for car, private bus and light commercial vehicle (class 3, 4, 5 and 7 vehicle) MOT tests.
www.gov.uk
