A good place to start is to look at the wiring diagrams for your 2004 E53
I6 (not V6) and check out what is common to your failure points.
For instance, here is the drivers heated seat wiring...
https://www.newtis.info/tisv2/a/en/e...-side2/hQ9SNGN
And here is the sunroof wiring...
https://www.newtis.info/tisv2/a/en/e...s-roof/qN5N5B4