I will venture an answer here based solely on my knowledge of the 90s SCs, as I own only the in-line 6-cylinder SC300s, not SC400s, but there is a lot of design similarity and commonality. If you're looking for the fuse boxes on an early to late 90s SC400, see the question "Where are the fuses for a 92 SC300?" (or something like that.) I bet they're in the same place. Under the hood, driver side, and floorboard driver side under the dash near left foot clutch / brake placement behind the panel.