Depending on what you need to tow with your towbar, electrics need to be added.
Single socket (12n)
This is the minimum required to operate the road lights on your trailer, cycle carrier or caravan. It will operate all lights except the reverse (you will need a twin or 13pin socket to get a reverse light). In the past this was done by simply connecting into your cars lighting system and effectivly sharing the power from your car lights. Although perfectly acceptable 10-15 years ago due to the complexity of modern car electrics this is no longer the case, wiring should be fitted with an aftermarket bypass system or better still a dedicated vehicle loom.
Twin socket (12n + 12s)
If you are towing a caravan you may want to have a twin socket fitted. This is not essential (unless you have an ATC stability system) but it will run your caravan fridge and charge your leisure battery as you’re driving.
13 pin socket
Essentially this is a twin socket combined into just one. If wired with the correct relays will have the same functions as a twin socket. This has become standard on new caravans and quite a few trailers too.
Towing electrics can always be changed, added onto or converted so don’t worry if your towing requirements change.
Towing socket converters
These are used to convert your electrics from 13pin-twin, twin-13pin, 13pin to single or single to 13pin.