rear brake lights staying on
 

2001 x5 E53. Ignition key on/engine run position, rear brake lights stay on constant. Ignition key on/acc position, rear brake lights work normal, corresponds to position of brake pedal, on/off. How do I diagnose this one?

Pull the panel by the pedal down, and push the switch forward. They sit in a ratchet holder and move occasionally.
This shows you how to adjust/replace BMW X5 Brake Light Switch Replacement (E53 2000 - 2006) | Pelican Parts DIY Maintenance Article

Actually, I just re-read your post and have no idea. But google does.

Okay, wait. Key to Position II (RUN), the brake lights are always on, key to Position I (ON) and the brake lights are off until you press the brake pedal?

This is important...
Are the brake lights on, or the running lights? Lights are on when the light switch is on, the Brake Lights only work when the brake pedal is depressed. Are you confusing normal lights and brake lights? Brake lights should not operate with the key in any position except Position II (RUN), and when the brake pedal is also depressed.

Brake lights and running lights all go through the Lighting Control Module (LCM), so you could be having trouble with the LCM. There was a complaint a few months back on the E46 boards where the switch on the brake pedal was a problem. It's operation is not what one would expect, and as I recall there was a fuse that had failed, without the brake light fuse the brake lights are always on. The confusion comes from the wiring that passes through the LCM. Normally a bad fuse keeps lights off, not on.

If you PA Soft software on a laptop you can look at live data for your lighting. It will tell you if the brake switch is detected as being on or off.

Rear brake lights
 

you are understanding this dilemma correctly. Key in run position, brake lights on constant. This includes the third brake light over rear window. With key in position 1, I can see Brake lights working normal response to brake pedal. on/off. (reflection on garage door)

Sounds more like an ignition switch problem.

Update. Made a little headway. Asking what changes w/key in acc, and w/key in engine run position. Checked voltages and grounds at Light control module (LCM). All looked normal with one exception. Found battery voltage at pin 47 with key in run position, engine off. This wire runs between the ABS/DSC Control module and LCM. Looking at wiring diagram it pertains to Brake Light Activation (Hill Descent Mode). Why voltage when the engine isn't even running? I'm not using cruise control. I removed the wire from connector to LCM. The brake lights are working/corresponding correctly to brake pedal position, on/off, no matter key position #1 or #2. Yea! Don't congratulate too soon though. A new dilemma popped up. With the engine running, the tach dropped to zero, and the engine temp gauge pegged at high temp. Engine was cold for sure because I just started it. I realize the wire at pin location 47 and this new dilemma may all be connected. Suggestions?

I don't suppose this is your scenario? Excerpt taken from : https://www.newtis.info/tisv2/a/en/e...-right/XTMlhsE

Would help if you identified your vehicle, though LCM function is probably universal across the years / engine options.

Functions, general

Diagnosis as well as communication with other control units takes place via the I-bus (E38/E39 high) or K-bus (E39 basic).

In the event of the control unit or one of its peripheral elements failing, an emergency operation facility maintains following functions.

- The outer rear lights (no licence plate light) low beam light, are switched on at "terminal 15 ON" irrespective of the position of the light switch.
- The left and right brake lights are switched on at "terminal 15 ON" and the brake light switch operated.
No communication via the I-bus/K-bus, i.e. also no diagnosis, is possible in emergency mode.

If a trailer coupling is installed in the vehicle, the lamp circuits of the pulling vehicle with a trailer module must be disconnected from those of the trailer. The LCM is connected to the trailer module via a data link.

A diagnosis program is provided for all 3 function spheres of the LCM.

Put the wire back in place and see if the new issues go away. I understand that the initial problem cleared up and this is what you want. but since clearing one problem caused a new one to appear, you need to see if the cure is more deadly than the original disease or if the new problem is actually a new problem all on its own.

Also, instead of looking at the lights glowing against the garage door, look at them in a window instead. Find a commercial building with glass that is low enough to see the lamps, then you can actually observe what lights are on and which are not. Of course, you could employ the assistance of a helper to depress the brake pedal as you directly observe what the results are.