From The E28 Wiki
By Wiseguy, Mon Mar 06, 2006
Original thread: My OBC1 Went dead (Pre-85)
Problem: My OBC1 Went dead (Pre-85)
Solution: Check the fuse that's INSIDE the OBC Computer, located underneath the steering column. Inside that silver box is a small fuse (I always used SFE4 fuses from Radio Shack) in an inline holder. I bet it's blown.
