The international code for the supplementary towing socket is:
1 (L) Yellow— reverse light
2 (54G) Blue—spare
3 (31) White— earth
4 (R) Green — accessories or battery
5 (58R) Brown —warning light
6 (54) Red — refrigerator only
7 (58L) Black— spare
A caravan or trailer must, by law, be fitted with certain warning lights. These are wired up to ...