Well then I guess it's a 50/50 shot as to whether or not it is needed. When I first installed my OEM hitch wiring I didn't have time to program it that day and it stayed undone for a week. I tried plugging in the trailer, the lights didn't work and the rear PDC still came on beeping. (on an 03 mind you) After I performed the retrofit it all worked perfectly.

So between my and JCL's experiences I would say just try it. :D If it works, carry on. If it doesn't work, you already know what to do. :thumbup:

I found out just after posting that the wire harness was not in the box WTF...

There was only the white square connector, the black round plug and the metal bracket, I tough maybe the wire is already hidden somewhere underneath the spare wheel, but it's not, excuse my ignorance but sometime you see a pics and think this is what you will get. I'm calling them right now and hope they will ship it free of charge since it's their mistake.

i hooked up my hitch and wiring a few weeks ago and i did not need to program it. all i did was remove the fuse for the module before i installed it. when i finished i put the fuse back in and the trailer plug was tested with a test light and worked fine. i also have a plug that goes into the trailer plug that acts as a reverse alarm and that also worked fine once i was done. so im not doubting that i needs to be programed but like Weasel said maybe its a 50/50 shot.

you should have gotten it with everything else. that peice itself is about $95.00 from ECS and you cant do anything without it. i would deffinitly call up and make sure they take care of the sittuation. GL.

I called Bavarian Auto Sport and I was right they forgot to put the wire harness in the box, so they are sending me one free of charge. Good guys and great service even though it should have been in the box at first, the error is human so no complaint here.

I was reading the instruction and they suggested to unplug the battery prior to the installation, I guess removing the fuse would be the equivalent but I wont take any chance and follow the instructions but that wont be before another week tough.

Since we have had various experiences of needing reprogramming or not, even on two '03 models, I wonder whether the software version the vehicle is on has any impact on the need to reprogram for the wiring harness. My vehicle was never flashed or changed to a newer version, while I am sure that Weasel's has been updated. Just an idea.

Well according to BMW's instructions for the euro hitch it seems much clearer than 50/50:

Weasel
Will the coding sort out the flashing lights when the X is switched off?

I installed OEM hitch on the 2006 4.4i with parking sensors.
Trailer lights do work and Parking sensors are disabled when trailer is attached with no programming. Parking assist can not be turned on once trailer is connected.

Just for clarification as I just installed the hitch a week ago on my 2005 and did not take to the dealer to program - the trailer lights work (which I would assume would work whether the dealer did the programming or not) and the PDC seems to disable when my trailer is attached (non-brake so can't tell if braking system is functional and hard to tell whether the trailer sway control is functioning or not? What gets activated by the dealer "programming"?