Strange trailer light activity...

[TowX]

So I had the Uhaul trailer hooked up in my driveway the other night. While unloading it, I noticed that the trailer lights would flash very lightly every 15 seconds or so. I checked the truck to make sure the lights were off and they were. Doors were closed and interior lights were off too. I had to unplug the harness from the truck for fear of the battery running down. All factory wiring components.
Anyone else have this happen? It's just a data sample of 1 point, but I can't imagine it's anything to do with the trailer. Trailer doesn't even have electric brakes... has hydraulic surge brakes. Do I have a defective wiring module from BMW?

[jpm4.8is]

[Dubz]

I also have the same problem with my jet ski trailer, but I have no idea what is causing it to do that.

[surgeondress]

I have a 20' travel trailer, a boat trailer, and a 5x8' cargo trailer. Only the travel trailer and cargo trailer have LED lights, the boat trailer has regular incandescent bulbs. ALL THREE TRAILERS have this problem you've described, AND......all three also go into a triple-speed fast blink rate when using the turn signals. The boat and cargo trailers use the 4-pin straight adapter, while the travel trailer uses the 7-pin circular connection. Others on this forum have related this problem to be due to either low-voltage errors from LED lights on the trailer OR a missing or aberrant ground wire (none of my trailers have ground wires...). Most BMW dealerships appear to be absolutely clueless about this. One member on this forum alluded to some sort of adapter that BMW made which fixed this issue. Again, no part number was given and BMW NA and my local dealerships are clueless. What I can tell you is that I've left my trailers connected for days or weeks at a time on trips and these blinking trailer LED lights have not affected the battery at all. The only benefit I can fathom is that it looks to others like your trailer has a security alarm on it. Go figure.

[TowX]

Thanks all. At least I'm not alone. I was using the 7-round plug which is supposed to have a ground in it.
I also had the triple fast flashing blinkers. I'm used to American SUVs which will blink too slowly but that's rectified by changing blinker relays. Might try that to see what happens.
Next step- wiring the electric brake controller then buy a new race car trailer.

[JCL]

I have never seen the 15 second flash, but have read about it. I believe it is the BMW electrical system checking voltages, but am not sure. I equated it with the LED trailer lights, but perhaps not so given surgeondress' post.

I have rented a lot of U-Haul trailers. I have had the fast blink on the turn signals many times, but it isn't consistent even when towing the same trailer, it comes and goes. I found that a separate ground wire to the trailer (so that you are not relying on the hitch receiver for the ground) fixed it completely. That ground wire clipped on to the vehicle, separate from the 4-wire connection. I equate the fast blink with a high resistance from a poor ground. I am very familiar with buying HD flashers for North American vehicles, but found that with a good ground connection, I could pull a trailer with lots of lights without the turn signals blinking fast. I would at least try a separate ground wire before changing the flasher.

[surgeondress]

TowX,

Good luck with your electric trailer brake controller installation. There are two very good Word documents on this forum on how to do it with the Tekonsha Prodigy. It took me the better part of a day, but I morphed the two into what seemed like the best of both methods, ultimately using the passenger side light control module for the brake signal wire to the unit. It definitely controls the four trailer brakes well, but I've had an issue with that too. The triple speed blinker rate for the turn signals also intermittently turns the brake controller current on and off as well while slowing down (and causing the trailer to jump), essentially making it impossible for me to decelerate smoothly and reliably unless the turn signals are off. As I said, this is intermittent and independent of towing speed or magnitude of deceleration. It may happen at one stop, and not the next. It may even sometimes trigger/pulse the brake controller at steady speeds when only changing lanes. Even the trailer shop I took it to this past week couldn't find a cause of the problem, despite seeing the problem in action.

JCL,
As you recommended, I wonder if running a separate ground wire from the trailer light cable to the X5 frame might fix any or all of these issue. I may investigate that this weekend....

surgeondress

[X5Dawg]

I don't have this problem, but then again, I used an aftermarket wiring harness and not the BMW one