Faulty trailer lights are not only a nuisance to following traffic but are also downright dangerous. Often the fault lies in the plug/socket connection or the cable fittings to the plug/socket . Any plug/socket which is suspected to be faulty should be renewed. This job is not too difficult even for a beginner but identifing the correct wiring colours and terminals often puts people off this job. Terminals are numbered using standard systems and either one or both systems will be printed around the teminals

system “A” “B” Wire colour Operation

L 1 Yellow Left hand indicator

54g 2 Blue rear fog light

31 3 White Earth

R 4 Green right hand indicator

58r 5 brown right side lights

54 6 red brake lights

58l 7 Black left side lights

Once the wires are connected a coating of battery terminal gel will reduce corrosion on the wire ends and clamping screws, also always fit and tighten any cable grip or gland nut. Other faults common to trailer lights can include, damaged cables, blown bulbs, corroded bulb holders or corroded joint boxes. Disco type faults , eg. indicator goes off when brake is pressed followed by all lights flashing, is most likely to be a problem with the earth connection on either the trailer or towing vehicle. Remember the towing vehicle could be at fault so check for output at the socket using a multimeter or a test lamp.


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