The power seat diode (V1) is a two prong little box in the fuse/relay box. It is in the row closest to the fender and is at the end toward the cabin. It is next to the lighting module. The part is # 000 540 42 81 and lists for around $7.25.
It should pull straight out and be easily testable with an ohmmeter. It is the relationship between the diode and the bulb lighting through fuse 2 that makes this logical. Anything that accidentally made fuse 2 or 1 hot with term 15 off (key off) would turn on the light. The Diode just makes sense as the other users have no logical way to backfeed.
Bosch Master, ASE Master, L1
33 years MB technician