"Check Trailer Lights" fault on dash
 

I've never attached a trailer to my X before and assumed that the factory fitted tow-bar and connector were in good working order. The PO said he used it to tow a trailer with bikes for his kids.
I've done quite a few upgrades in the two or so years I've owned the car, including fitting LED tail lights, which look great and seem to work okay (with a bit of flicker on the park lights though).
Recently bought a new trailer that came fitted with LED lights. Towed it with another vehicle and all the lights on the trailer worked fine. Two days later, I hooked it up to the X and had my wife check the lights on the trailer before we took off on our planned trip. Indicator and brake light illuminate at the same time when indicating, no park lights and other weird things (indicators and brake lights both come on when depressing brake pedal).
Yesterday, I inspected the plug and pins, chased the wiring from the trailer plug to the connector in the wiring loom where the spare resides and cannot find any break, corrosion or whatever. Now I'm wondering if the LED tail lights I fitted last year may be the problem? Anyone with similar experiences?

It's unlikely that the LED tail lights are causing the issue you describe. I would suggest you check the wiring in either the trailer or the adapter - not for corrosion or breaks but check the connections are on the correct pins.

The issue sounds like incorrectly terminated trailer wiring or a short from one circuit to another.

Trailer wiring seems to be fine, as I towed it with our Landcruiser when we picked it up and all lights on the trailer worked as they should.
PO did tell me a few untruths about the car, so I'm now thinking there may have been a problem with the trailer plug on the rear of the X all along.... I have not yet pulled the plug apart or tested for correct connection to pins - that was my next step... I think I'll have to visit my friend who is an auto electrician to check it thoroughly...

I guess you have the trailer module fitted (as the CC on the dash is warning you of an issue) but does the loom look correct or are the trailer lights running off "vampire taps" from the vehicle lights rather than from the correct connector in the boot (trunk)?

I had a similar issue when I first hooked up a (known good) trailer to my X5 with "factory trailer wiring". The PO had fitted a bunch of extra wiring for an electric trailer brake and had not addresses the lamp monitoring problems caused by disconnecting the factory wiring. It took me a while to figure out what they had done and return it to normal.

When it was "faulty" the CC gave me warnings (Check Trailer Lights) and occasionally the cars indicators went mad etc. - all very odd. All good now - no problems.

My old thread here: -

http://www.xoutpost.com/bmw-sav-foru...tify-pins.html

(can't call it a thread really - just talking to myself! :cool: )

I downloaded the PDF someone posted about fitting the towbar including the wiring diagram etc. From what I can tell, all is fine, with an OEM connector where it should be and no 'vampire taps'. This makes me think that whomever wired the plug may not have done so correctly, or there's a short in the plug perhaps.
I unbolted the plug from tow-bar assembly, pulled the cable down as far as possible to inspect same and also looked inside boot/trunk, disconnecting plug and inspecting for integrity. All seems to be fine from visual inspection.
I've just spoken to my mate the auto sparky and booked in to see him on Monday AM - he's not cheap, but very good. Hope we can sort things out, as trailer plugs are a PITA to rectify by yourself.

Do you have the flat four connector on the trailer and the standard round connector on the X with an adapter that allows the flat four to mate up with the X round connector?

Check the adapter, you could have an adapter that isn't wired correctly. I used the factory BMW connector and never had any problem, whereas with some other connectors some of the trailer lights wouldn't work.

No adapter to the factory fitted outlet. Our trailer plugs here are a bit different to the ones you use in the USA. They are round and have 7 pins, but not all are used for a standard u-haul type trailer (one spare pin is + supply for 12V internal power for a caravan).

Given the symptoms (several lights illuminating at the same time) I'm leaning towards an earth issue. It'll be much easier to diagnose with a second person assisting me... Will report back when/if it's fixed tomorrow.

The problem is the LED taillights on trailer will not work with e53
You must buy a canceller device from etrailers.com.

Sent from my Nexus 5 using Tapatalk

While this is true and will likely explain the "Check Trailer Lights" warning, it doesn't explain the issue with multiple circuits being activated simultaneously (indicator and brake circuits tied together somehow). This can sometime occur with a back earth and lamps in one circuit "back-feed" another, LEDs are omnidirectional and shouldn't do this.