They are lights that go on your trailer to show your turn signal and brake lights. Reese Hitches has all of the top brands if you're in the market for some: http://www.reesehitches.com/product_categories/trailer_lights
The trailer has a dead short in that right side brake light circuit.
It's a green light that should flash once every time you put your signal light on (either direction). This light tells you that the trailer wiring system that was built into the Disco is working properly. When you tow a trailer and connect the trailer lights to the LR wiring connection next to the hitch, the green "trailer" light on the dash should flash in sync with the signal light arrows every time you put on your signal light. This is telling you that your trailer lights are working properly. If the green "trailer" dash light does not flash, then you might have something wrong with the trailer lights or with the wiring. Unfortunatly Land Rover abandoned this feature on the Disco II.
On a light trailer or small boat trailer you remove the bearing cap, pack it with grease and re-fit it.
Dead short in the trailer wiring or one of the trailer light sockets.
Lights are always required to be installed on a boat trailer. This is so no one runs into the back of the trailer, especially at night.
how do I install a trailer lights to a Honda 1998
short circuit on trailer light wiring
Somewhere rear brake light area.
How do you install trailer wiring on a 2009 civic
poor ground wire
Before entering a trailer dock, you should verify that your light wheels are docked.
Double check that you have a good ground on the trailer and on the vehicle. White wire should be connected to bare metal. Also ensure your trailer tail light bulbs are not twisted in their sockets.