2014 SD4 with genuine JLR trailer wiring loom (plug-n-play version).

Today noticed that none of trailer lights were working.
But all trailer lights worked when I ran earth from trailer bulb connector earth through trailer chassis and back to car via tow ball !
Thus I diagnosed a bad earth somewhere.

Using a bulb and wire to earth I started by testing the car's 13 pin socket. All OK or so I thought.
I have a 13-to-7pin adaptor as the trailer is old. Adaptor tested OK
I then plugged in the trailer plug and started to test the plug terminals having removed the cover. I then noticed no RH side power.
Going back to the car's 13 pin socket I've now lost all trailer RH power to brake, tail and indicator lights. LH side is fine.

All the car's own lights are fine.

Does the car have separate fuses for RH and LH trailer lights? Can't see them in the owners handbook list of fuses.
Have I blown some electronic module somewhere ?

Im not sure what has happened. Gave up as too dark to see - I hate winter.
Any advice gratefully received. Jules

This is rather weird

Just been out and did a quick re-test and all the pins on the car's 13 pin socket are working EXCEPT the RH indicator .

Not sure what's going on.

Will check the looms connection in the boot tomorrow.

Also found the loom's installation instructions from 5 years ago.

The only fuses added are F48 and F67 for 12v power and switched 12v power respectively - both 15amp. So no indication there as to what is wrong. Jules

Think Ive sussed it.

This morning all is fine - all the 13pin car terminals are working normally again.

The car must have a module somewhere that protects the car from shorting of any of the trailer circuits. It shuts the circuit down for a period of time (I dont know what governs this time period) and when you restart the car all the circuits are working again.

I tested it (inadvertently) by removing a trailer indicator bulb and shorting the terminal transiently. The indicator circuit went dead. A few minutes later I restarted the car and the trailer lights are working again.

Note to self - disconnect trailer from car when changing bulbs. Jules

Jules
I know this is an old thread but I’ve had some weird things happening to my FL2 when the van is connected. At first turned on lights of car and van side went on then off. Wouldn’t come back on until turned car off on

Everything else worked fine

Took it on 2 hour drive Got to site and couldn’t unlock tailgate ?
Turned off car and lost everything. Couldn’t detect smart key. Hour or so later cleared it’s self
Weird
Next day battery flat

Will explore more when home