Sounds like a bad ground to me. Trailers are NOTORIOUS for have ground problems. Make double-triple-quadruple sure that: (A) The tow vehicle plug is properly grounded to the vehicle frame (B) the trailer plug is properly grounded to the trailer frame. Even though both can appear to be OK, a flake of rust or paint will totally disrupt the circuit.
I had this same problem on my 2000 Ford e 150 and after going over everything several times I finally found that my fuse for the running lights relay going to the pigtail that was put on the van when the van was built so its from manufacture, was fuse d under the hood on the drivers side was partially cracked so it looked like it was good every time I checked the power going to it but I put a knew fuse there and my running lights started working and I was so close to taking it in witch would have cost allot more than the price of a fuse, the c and d fuses that go to the trailer light operation are from manufacture so not sure where u can get them...anyway I just used my c fuse and put it in my d slot cause my trailer has no backup lights on it so i did not need it in that spot.
I would check the running lights for one with a short. I had the same sort of thing with my trailer and I spent way to much time troubleshooting the brake and signal wires. Turns out a running light bulb connector was grounding out on the trailer and messing it all up.
There are separate fuses for trailer signal lights in main fuse panel
signal lights not working.
signal lights
This year of truck has a separate circuit for the trailer turn/barke/tail lights. Look under the hood, under the fuse box. Look for the trailer fuses on the fuse directory
Short circuit , maybe ????
Hitch the trailer. Connect the lights. Start your car or truck. Turn the turn signal on. Get out and go behind the trailer. See if they blink. Repeat for the other side.
Im not sure i under stand your guestion, but it sounds like the trailer wireing is wrong. The wires on the trailer should be wired like this. White is ground, Green is right turning signal,Yellow is left turning signal,Brown is running lights, Black is brake lights. I hope this helps you.
Left sinal not working in trailer hook up ?
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.
Vehicle side, Brown, running lights Yellow, left signal/brake light Green, right signal/brake light Black, ground Trailer side, white is ground
If all the running lights (front & back) are not working I'd start by checking the fuses then onto the headlight switch