Hi all, I am excited to say that I will be upgrading my car to Sylvania LED fog lights (H11). These Osram Sylvania lamps I got are made in Italy and feature a high quality heat sink rather than a cooling fan for improved reliability. Please stay tuned for some pictures here on my LG automotive album 
As excited as I am to install my new fog lights later this month, I do have a few questions...
I've heard that some automotive LEDs can draw power and run at minimum brightness while the car is running and possibly when the car is turned off. This could lead to battery drainage. I haven't had this issue personally, but I was wondering if it is a common concern with LED upgrades?
Will LED lamps work with steering responsive fog lights (i.e. when I turn left, the driver side lamp illuminates and when I turn right, the passenger side lamp illuminates)?
The LEDs can not draw power when they are disconnected.
But it is a common thing in the cars to maintain many ECUs powered, just in a sleep mode where they have minimal consumption (most car makers have 100uA limit for accepting a new module design from supplier, anticipating few 10's of them in a car), so few mA cosumption of an entire parked car is normal. It is still way less than the internal battery leakages, so big issue.
But there are two problems:
When there is some defect, mainly in the ocmmunication networks, some modules may not enter the sleep mode and remain active and draw way more current.
And other problem affects mainly the diagnostic, but also is the main cause for the drained batteries: Many, even rather high power, things activate already when you unlock and mainly open the door (fuel pump flushing out the air from the system, glow plugs warming up in diesels, sometimes oil pump pregreasing the engine,...; all to allow seemingly immediate prompt start of the engine), some remain active after the car gets parked (water and oil pumps to continue cool down mainly the turbo,...; to prevent the heat from the otherwise very hot running components destroy parts not designed for the heat - e.g. turbo shaft seals and bearing can can be easily destroyed by the heat from the turbine wheel normally operating at the exhaust gas temperature), which first makes the diagnostic of the battery drain difficult (you have to first wait before these things shut down before taking any measurement) and second seemingly innocent messing with the car (mainly just opening the doors) may actually drain the battery pretty soon.
That of course bring sensitivity to defects noone cared before: E.g. a glitchy door closing switches may easily drain the battery overnight - cause the engine prepping itself for start (pressurizing fuel and oil systems, warming up glow plugs,...) many times at night.
