Electrical/Engine problems

[jerry hempler]

I have a 2000 X5 with a couple of problems.I live a long distance from the nearest dealership, and also I am a professional mechanic. Firstly, the tail lights on my vehicle sometimes don't work properly. Specifically, the right hand signal/brake light gives the most trouble. Sometimes it works, and aometimes it doesn't. I checked it and it does not get power sometimes. I noticed that BMW is low voltage for the tail light, and then full voltage for the brake. This tells me that there is some kind of a module that is malfunctioning. What I would like to know is where this module is located, and if there is way to positively diagnose it. The bulb is fine, I have had it all apart to check it several times. The second problem that I have is an apparent fuel starvation problem. The "check engine" light is on, and a check with my scan tool indicates a lean condition. It is not noticable under normal driving conditions, but when full power is required I can feel it is starving. I checked the fuel filter and also replaced it, but this made no difference. It has been like this for quite a while. I am inclined to think that the fuel pump might be weak, (but I think this kind of unlikely as they usually just stop working altogether), or maybe the fuel pressure regulator. Or maybe it is something completely different that I haven't thought of. Clues or specifications would be greatly appreciatd