2006 525i Straight 6 motor. Which is the cylinder order ?
 

Just wondering and basically want to make sure I have it right. Is the order of the cylinders on a 525i 1 2 3 4 5 6 starting from front to back (front being nose of car) ?

yes

More broadly, the cylinder furthest from the transmission is #1. That works on V8s too, since one bank is offset forward of the other.

I don't believe it is 1 2 3 4 5 6. I remember troubleshooting this quite extensively with BMW software. In DIS i had the ability to kill one cylinder at a time and read the code. I unplugged each coil on another BMW and read the codes and the unplugged coil didn't match the cylinder that threw an error. Do some more research before talking other members opinions unless they can back it up with documentation.

I believe cylinders are labeled 1 thru 6 from front to back. However, firing order is different (not 1 thru 6).

Cylinder numbering is from front to rear; 1 at the front and 6 at the rear.
Ignition firing order is 1-5-3-6-2-4.