Since this confused me too at first I thought I'd just add that there is a note above "table a" on page 971-2 (in the Bentley manual):

"In the wiring diagrams fuse positions 1-3 in the engine compartment fuse/relay panel may also be referred to as fuses 22-24."

Note also that fuses 22-24 are quite the opposite between 78-80 and 81-83 models.

Cheers, Björn

For me this was simple. I checked the three fuses at the rear till I found one whose current was switched by the key. I wired the MSD there.