bmw tailight mod

im working on the BMW tailight which is driven by a LCM - light control module, up front . this powers the lights directly at the rear end. i have a single 21W bulb (1 filament only) which acts as the brake light and running light. the running light seems dimmer abt 4W and then when brake applied its bright, 21W.

how do they do this in a single bulb? i need to separate the 2 functions as the new tailight has got separate bulb sections to cater. i will need one brake light output 21W and another 4/5W running light output all from that existing pair or just the brake light signal will do (the running light can be sorted differently).

the LCM also throws an alarm if the bulb is out. how do i mod this to prevent the alarm.

thks for any help. 

How do they do it? They probably chop (PWM) the signal. Simple. How would I do it? Without knowing how the LCM operates, I'd hide the bulb somewhere and measure its current (loop transducer maybe? ~$20). If it's >1A (21W), the stop is on. If it's >0 but under 1.2 to 1A, then it's a running/tail light. Else it is off. You could substitute a 21W resistor for the bulb (it'll get a bit hotter, but won't be as visible...) and you might be able to insert a small resistance to make a shunt ammeter (measure the voltage across the resistor where I=V/R). The shunt could be part of the 21W resistor. (Remember, PR=VV; P=VI=IIR.)

my dad have a 1999 328i convertible and has been told that he need to replace the tail light assembly due to corrosion. we have searched the internet and can't find any info on replacing the assembly. I find plenty of info on replacing the tail lights themselves, or the brake light switch, but not the whole assembly.Can someone please point me in the direction of an explanation (or pictures etc) of how to do this? I can't seem to find a thread on this anywhere. Or if someone can explain the procedure I would sincerely appreciate it.

Links don't work here.... It should be that simple that you shouldn't need directions. Usually it's the removal of nuts from within the boot/trunk after cable disconnection. You may have to move or remove any lining or plastic shroud to get to the nuts (or bolts) which are usually around 10-12mm (maybe try 3/8" for 10mm or 7/16 for 11mm etc). Usually ~8 nuts - one in each corner and then "enough in between". Be careful of any other screws that might also be holding the assembly on, though if it's a full replacement, damaging the light assembly isn't a problem - sometimes final removal can be difficult if sealant used to stop water leaks (or "stuck" gaskets). I removed a 328 assembly a while ago and don't recall any problems - except the primitiveness of its construction (galvanised exposed bus bars). I don't recall having to remove the lens first (to get to bolts etc) nor any tricky screws... But inspection of the new assembly should show where the nuts/bolts are etc.

In fact a quick search yielded www.khoalty.com/blog/bmw-e36-tail-light-install-replacement-diy/. I only post that link for its instruction which is quite good - NOT for its "We offer them at a ridiculously low price..." plug (which may negate your link at "StationaryBusbar" if that was a plug).