Leaderboard

EL doesn't show the circuit, but it does show (roughly) where every electrical plug in the truck is located, down in the harness layout section. The '90 manual shows 211M below the fusebox, A pillar/driver's kick panel area as level9 described. The '95 manual shows it on the passenger's side. Probably a round-dash thing. I would expect yours to match the '90 manual. This is what the breaker looks like, if that helps.

The VG33 is pretty reliable. Timing belt should be done if you don't know when it was done last. There's a writeup here, and you can get the service manual from Nicoclub, which will also explain how to chase that P0115 code. P0300, might need a general tuneup. Maybe clean the MAF and throttle body while you're in there. Standard fluids/filters. I don't see rust in the picture, but I'd have a poke around the front strut towers to be sure that they're solid.

It should look something like this: https://www.ebay.com/itm/264635006128 The FSM shows it left of the fuse block - says "Beside Fuse Block" . It's in the BF (body) section of the manual, not EL (electrical) because.. special snowflake . Possibly next to the ground wire screwed into the chassis behind the kick panel. It may be stuffed in there with other stuff (door chime, etc.). At least on the hardbody forums, that's where it is. Some have it on the pass side kick panel. Maybe different years. It looks like it may also have its own fusible link connection on the battery so you may also want to check there (no melted wires, etc.). Again, special snowflake... Wiring: white/black + white/green -> circuit breaker white + white/black -> fusible link