One side light on the caravan refusing to come on all checked out but fault appears to be on the Range Rover electrics so into our local auto electrician first thing tomorrow morning.
When you say ‘one’ sidelight, do you mean just one light or the entire side ie. all of the left or right lamps out. The reason I ask is that caravan lights are sided, from the tow socket to the fuse and then on to the lamps. So, if the left hand side fuse/wiring etc is faulty, it will take the entire left hand side out (stop lamps excluded as they are separate) and likewise for the right hand side.
A single lamp out usually signifies a blown bulb or poor connection, usually through furred up bulb to terminal connection. The bulb is easily tested with two bits of wire and 12V supply. The same can be done by touching the same bits of wire to ‘cleaner’ sections of the bulb terminal metal parts.
Are you running 13 Pin ISO tow socket or the earlier style 12N and 12S twin sockets. The principle is the same regardless. One lamp out equals problem local to that bulb. Whole side out equals either caravan fuse to that side, faulty/corroded/dirty tow socket plug or vehicle socket, hence why I ask if it’s just one lamp out.