[Annolago]

First of you need to be better in your description of the problem. You have a fault with the level system but don’t have a scan tool. How are you then told there is a problem. Is via the in car message system or are you guessing or ???
On the lights not working- yes the wires going to the rear hatch tends to brake. After all they are now 15+ years old in your car - however I am really confused about how a subwoofer could have anything to do with the problem. Are you hinting that you are driving around playing music so loud that you are braking the bulbs? If you’re doing that then start saving for hearing aids.. Getting back to the wire issue, you can get a repair cable set to fix the broken wires. Go with a name brand to ensure decent quality cable have been used and not just any cheap set from eBay.
Strongly suggest that you like all new users to the BMW E60 read the “star here” permanent posting. In it you will find a lot of good information on how your car works and how to keep it running. Also if you have a laptop then get a OBD2-usb cable and at minimum a copy off INPA so you can accurately read error codes. Very difficult to guess so most People’s first answer will be what codes you have pulled from your car.
Best of luck

 

[Annolago]

I am sorry but I don’t have a car equipped with air suspension so cannot help you. Have you checked the document in the posting I mentioned above? It is easy to check if the bulb is gone, if you have access to a multi meter and can check resistance.
I would also suggest looking up your car on realoem.com so you can look up part numbers or even get an idea on how things are put together.
Also Newtis.info contains all the repair guides from BMW. Really great source of information.
But again, all is in the “Document ’ that is in the suggested posting mentioned above.