Brake lights not working on trailer

daus318 · #1 06-03-2009, 03:32 PM

I had my hitch installed by BMW a few weeks back on my 35d and it tows great but the problem is that my trailer brake lights don't work. Both turn signals work and the parking lights work. Also, all trailer lights strobe (like a warning) when I plug in the trailer. Any ideas?

durnie · #2 06-03-2009, 09:18 PM

Quote:

Originally Posted by daus318

I had my hitch installed by BMW a few weeks back on my 35d and it tows great but the problem is that my trailer brake lights don't work. Both turn signals work and the parking lights work. Also, all trailer lights strobe (like a warning) when I plug in the trailer. Any ideas?

If your trailer is running led lights you will have problems with warning lights as the system thinks there is a fault, I think because it draws less power.

Denalio · #3 06-03-2009, 09:44 PM

Are you using the correct adapter plug?

daus318 · #4 06-04-2009, 06:42 AM

Quote:

Originally Posted by Denalio

Are you using the correct adapter plug?

Not sure, it's the plug the BMW provided to me.

TetherEd · #5 06-09-2009, 01:32 PM

Daus,

Did you get this working / talk to the dealer? I am having the same problem with my 35d.

Ed

daus318 · #6 06-09-2009, 06:24 PM

Not yet, my dealer is in contact with BMWNA to figure out the issue. The only thing I know right now is that it's a computer problem. They said it's a "faulty module"

TetherEd · #7 06-09-2009, 07:17 PM

Thanks for the reply on this. I am really ticked off about having spent 65K on a car that has a jacked hitch install kit with electronics that don't work. Do let me know if they find the solution

Thanks!

Ed

watrob · #8 06-09-2009, 08:16 PM

You cannot use trailers that have led lights on them, that is all the problem is!

Ron07x5 · #9 06-19-2015, 11:43 PM

Quote:

Originally Posted by watrob

You cannot use trailers that have led lights on them, that is all the problem is!

Guess I should be happy I have a older trailer with non-leds.

JCL · #10 06-20-2015, 02:52 AM

There are two different issues being conflated in the posts above.

If the lights don't work on a new hitch and electrical install, whether brake lights or turn signals, the vehicle likely needs coding. Proof is often that the rear PDC doesn't deactivate when a trailer is connected, or that the rear view camera doesn't work in trailer mode for those vehicles that support that function. The vehicle isn't recognizing that the trailer wiring module has been installed, and so it isn't functioning correctly. Think of it as a plug and play CD newly installed in an older PC, which should be recognized on boot up but isn't. The solution is to code the vehicle to specifically know that the trailer module is installed.

A second issue is with LED trailer lights. Fast flashing, or continuous flashing when parked, can be a problem with the vehicle not recognizing the low current draw of LED trailer lights. There wasn't an OE fix until BMW came out with an update (referred to above) that recognizes LED lights. The easier fix is to buy the special LED light adaptor plug (round to 4 pin flat) that includes resistors to make the LED lights draw the same current as regular lights. VW sells it, as does U-Haul. Don't know if BMW has one, but haven't seen it. Not required if you have the BMW update for LED lights, or if your LED lights draw enough current to appear as incandescent lights.