The Ford Focus can be equipped with a class I receiver hitch which can tow a trailer weighing up to 907kg. In order to safely operate a trailer, you must install a wiring harness that connects the tow vehicle's brake and tail lights to the trailer. The Ford Focus is equipped with plastic electrical connectors behind each tail light, that must be separated to insert a trailer wiring connector in between them.
Loosen and pull back the carpeting in the back of the boot behind the taillights.
Remove the plastic wingnuts that secure the tail light to the vehicle's body.
Separate the taillights from the vehicle's body, but do not disconnect the wiring.
Examine the wiring harness on each tail light. There will be a plastic connector on each side that must be separated to insert the wiring harness connector.
Thread the trailer wiring connectors through holes in the body behind each tail light. Follow the instructions provided with the connector to determine which connector belongs in which side of the vehicle.
Insert the wiring connectors into the vehicle's wiring harness.
Push the taillights into position against the body and reinstall the plastic wingnuts that secure them. Be careful not to crush the wiring.
Route the trailer wiring underneath the carpeting in the boot, so that the trailer connector can extend out between the boot lid and bumper when in use, and be tucked into the boot when not in use.
Reposition the boot carpet over the tail light housing.
Position the wiring so that the trailer connector is not taut when connected to a trailer. When the vehicle turns, it will need some extra length in the wiring to avoid putting stress on the wiring.
Be careful when you route the wiring to avoid sharp corners on the vehicle's body, which can cut through the insulation.