When your brake light switch fails you will get a bulb out warning on your dash and your brake lights will be always on!
Your brake lights are turned on by the LSZ and each tail light is controlled independantly. Your brake light switch simply tells the LSZ what to do. If there is any failure in the control circuit, the default failure mode is such the LSZ is instructed to turn the brake lights on.
Your answers to the voltage question (irrelevant but are as follows)
While the car is on, and where 12v=battery voltage (sub in 13.5 or whatever/irrelevant)
Brown Black to ground should be 0v, brown black to 12v should be 12v
X1179 to ground should probably be 12v depending on the switch orentation, assuming fuse F9 is not blown (Climate control and steering wheel controls share same fuse) when car is on but brake pedal is not pressed, should be 12v. Unless it is variable resistance..
X181 might be variable resistance.. not sure.
While car is off:
While the pedal is up, there should be continuity between fuse F9 and X1179, there should not be continuity between X1179 (or F9) and ground
While the pedal is down, there should not be continuity between X1179 fuse F9, there should be continuity between X1179 and ground, there should not be continuity between F9 and ground
Per WDS (http://wds.spaghetticoder.org/en/zinfo/FOI0398FB-056613101.htm), my notes in bold:
Brake light switch
The electronic brake light switch only operates as from terminal R ON.
From when you turn the key to on
It has its own voltage supply.
Fuse 9
If the brake light switch is OK, it assumes a high-resistance setting when the ignition is switched off, i.e. it sends a signal as if it were operated. If this is not the case, this indicates a short to ground and the messages "brake light defective" as well as "rear right lamp defective" and "rear left lamp defective" are output or indicated in the pictogram in the instrument cluster.
This is X1179 they are talking about - So when car is off, switch is "open" - the brake lights should be "ON" while switch is "Open" (the reverse logic of what most expect but makes sense from a safety perspective) - Circuit is open when car is off because ignition switch opens circuit to entire fuse bus (not interesting unless F9 always seems dead, but doubt then you'd be complaining only of brake lights) - Basically, the switch being unplugged/missing should trigger your brake lights to be on. Since F9 is also connected to the LSZ, the LSZ can(and does) test the state of the switch before the ignition switch provides power to the upstream fuse combs
The light switching centre recognises the "operated" status if there is a break in the line. If is recognises the switch interrupted for longer than 10 s as operated, the light switching centre then also makes use of the vehicle acceleration signal. If a conflict is then detected, the above-specified error messages are output.
In addition to what I said above, if you are accellerating for 10 seconds while the circuit is open (like your pedal is depressed), you should get a bulb out warning - that means even if F9 was dead, you should get a bulb warning and your brake lights should be on/illuminated until you replace it because the circuit would be open.
::End WDS::
You say you have no bulb warnings - I would assume your switch is good - I would assume someone turned off the rear bulb monitoring and you have an issue with the ground in the rear tail lights
or your LSZ is toast
Are any other lights not working? Can you check F32, F9, F106 & F107?
http://wds.spaghetticoder.org/en/zinfo/E46_EF106A.htm
DIS/MODIC/INPA should be able to activate each individual light from the LSZ over the diagnotics port and tell you the state of the brake pedal switch... that would go a long way to diagnosing this issue quickly.
