IIRC in my '95 S420 is was in the trunk fuse panel above the battery.

With no familiarity with that engine my first suspect is the crank position sensor. It's not fun to get to in an M104 requiring removal of the starter or oil pressure sender. So I'd listen in the area ahead of the right rear wheel while someone turns the key to on (not start). There's probably a fuel line in the engine bay you can crack to check for pressure.

Sixto
98 E320s sedan and wagon