<Hi there!
on my bike the problem is the fuel indicator (AKA "fuel strip") in the tank.
Two years ago, while on the road, I started getting erratic readings about the amount of fuel in the tank. BMW blamed some additives in the fuel that may have short circuited the "strip", and replaced it for a new one at no charge. One year later, readings got erratic again. BMW guys said they would replace the strip again, as it was under warraty. Two days later they phoned to say they needed some more time cause they had changed the strip 3 times (2 were new and one from another bike) and none worked. A week later they still did not find out what was wrong. 10 days later they said it was my fault because I had too much "non original stuff" on the bike (one HID lamp, two PIIA halogens, and a set of Hella horns) causing the wiring to fail. As none of these accesories were connected directly to the wiring, but to the batt by means of relays I did not buy their "diagnosis", so I told them to disconect the fuses from these parts and to test the strip again.... AS EXPECTED IT DID NOT WORK!
A long weekend approached, As I had in mind to make a short trip on the bike, BMW returned it to me promising to continue the repair upon return. When I left the shop, the indicator was as dead as when I brought it in. The next day, after refueling it started doing some weird readings..... at the end of the day it was working propperly again. (??!!) 8 months have passed since and the readings from the strip are still quite accurate. BMW guys have no idea why it does work now.... and offered to take a look, but I didn´t let them! I know it will fail again, probably when I need it most..... but what else can I do?