A popular installation is the Universal 7 Channel Towing Interface Module. This system is usually cheaper than a vehicle specific kit, and whilst it acts as a buffer to prevent voltage surges and spikes affecting the towed vehicles digital circuits; it can also create faults occurring in the towed unit’s electrical circuitry that can damage the electrical circuits of the towing vehicle.
Some universal kits come with pre-cut cables and some additionally offer a Split-Charge Relay, which, for instance enables the caravan fridge to be active whilst the vehicle is towing, and will shut down once the ignition is switched off to protect the vehicle battery. This can sometimes be problematic with modern Start/Stop vehicles.
The towing interface relay must include a built-in audible device which buzzes when the vehicle's directional indicators operate, alerting the driver that the towed unit's indicators are working, as this is a requirement to comply with UK road regulations.
Most kits come with a variety of fuses, relays and sometimes connectors. As well as wiring, sometimes pre-cut, some fixings and wiring grommets. There many also be occasion where there is a need to ‘splice’ wires together.