Power TCU trough Ignition position -Battery Drain- Solved

[whizzkid23]

Well, it seems that the day has come for our 2005 x5 3.0i to start draining the battery because of a somehow faulty TCU unit. The bluetooth module (Fuse 74) seems to keep waking up the car from sleep mode every 10/15 minutes or so, drawing a 0.5Ampere for a few minutes. Result = dead battery after a night or two in cold days.

Long story short: Besides this power drain, the bluetooth module is working great and I love the quality of the microphone and everything else. I really would like to keep it in working condition.

The solution that came to my mind is to power the TCU trough a power source that is directly bond to the ignition switch position. Logic: Key turned = TCU powered, Key removed = TCU without power.

I could cut the original power supply to fuse 74 and steal the power from the rear lights, but I guess the LCM would notice a too high power drain. Maybe some of you have a smarter idea or approach on how to power this unit (obviously always securing the circuit with the proper fuse).