Twice a week I need to get on my knees te connect the electrical plug of my trailer into my car. Because the connector is for design/safety placed out of sight under the rear bumper.
When I have done that I need a second person or well placed mirror to check if the connection is working.
Also the connector of both the trailer and the car are sensitively for influenses from weather and mud. Also the connector of the trailer is often not correctly disconnected (by pulling the wire instead off the connector).

It must be possible to loose that wire and send the right signals wireless to the trailerlights.

You should think a small battery, a genarator in the traileraxis and a simple bluetooth adapter should be enough to realise this.

The bluetoothadapter in the car can be placed on the
trailerconnector or inside the car.

Redesign challange:
Connect a trailer to a car without making an electric connection by wire.