Trailer lights flash (dimly) and infrequently after shutting down the X5. Went back hours later and they are still flashing periodically.

Yea I made my own harness but I don’t see how that would matter.

The tech at the dealership worked with me several years ago to research what was going on with the use of LED trailer lights. This should address several points brought up through the course of this thread:


The BC (body computer) checks the amperage load in all bulb circuits to evaluate the presence of a burned out lamp. The BC knows when a trailer harness has been plugged in at the adapter and tests those lighting circuits as well. Since the LEDs draw such a low amount of current, the BC interprets them as burned out incandescent bulbs and tells the flasher unit to use the "rapid pace" interval as a signal to the driver that a turn signal lamp is not functioning.


I tried using additional LED signal circuit resistors that are available from several trailer lighting manufacturers, but found they deteriorated badly after a year's worth of lake immersion. So I installed a small, incandescent red marker light in series in the turn signal circuit on each trailer taillight and it cured the problem.


When the taillights are on in conjunction with the headlights, there was enough of a current load that the BC knew the trailer taillights were working.


As for the periodic flash observed in the LEDs when the X5 is turned off, that is the signal passed though the body harness by the vehicle alarm system. The LEDs are so sensitive that they are able to light up briefly when the alarm test signal is emitted. I haven't tested it, but I believe that if you disconnect the trailer harness from the vehicle when it is locked and armed, that the alarm siren may go off on the X5 letting you know that someone is trying to steal your trailer.


2002 X5 3.0 361,300 miles (Regularly towing 1300 pound PWC & trailer)

2014 428i 63,900 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird under restoration - engine dyno run in August

Interesting. Gonna try the latter right now.

Since they are LEDs, I wonder if I should be concerned about current draw over time? Else, I'll just disconnect the trailer from the X.

Alarm doesn't go off when I remove the trailer harness from the X5 with the alarm set...

Darn it! That would have been kind of a neat feature!

This thread is so old. I did t bother reading it all. But has anyone checked coding if trailer lights cold monitoring can be turned off. I turned off a shit load of cold monitoring in my car when I discovered coding. Don’t remember if trailer lights have CM.

:iagree: Try turning off cold monitoring in the tail lights and brake lights.

http://i.imgur.com/C2YDFvx.jpg

So what is the solution for towing a trailer that has LED lights when you can't modify the trailer?

I had to tow a furniture trailer yesterday and went to two different hire places. All of them have LED lights and my 4.4 won't show ANY lights at all on the trailer..... zip, nada, nothing....

I had to go all the way home and grab my work truck, clean it out and pack the family in it :thumbdown as a tow rig

Is there and adapter that can be connected to the X5? (I've got the round Euro 7 pin)

I haven't found any other adapter. i just live with the rapid flash if I have to use a rental trailer.


2002 X5 3.0 361,400 miles
2014 428i 64,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration - engine dyno run in August

I replaced my original incandescent trailer tail lights with LED units 4 years ago and have never experienced any of this.