Trailer connectors are used to link the electrical systems of the vehicle to those of the trailer or caravan. This is how the trailer or caravan can display the corresponding lights if you use the indicators, turn on the tail lights, use the brakes or fog lights. This is extremely important for the safety of your driving whilst towing.
If those behind you cannot see the signals you are giving them, this could, in extreme circumstances, lead to serious accidents. It is therefore important to make sure that you have the right fittings and connectors before you set off on a journey with a trailer or a caravan in tow.