Are you sure all the fuses are in and not blown? (Given you missed the fan fuses where missing, you may have missed some other ones too.)
You pretty much have to just unplug everything on the circuit one by one unit something starts working again.
Ideally you want a set of Factory Service Manuals, then you go over the wiring diagrams, identify the circuits that are effected. Note the fuses (there will be multiple fuses invovled in most things), then test that the grounds are good, and check what voltage they are carrying, you may find one fuse is lower than 12v, this is the start of a thread you need to trace.
Some manuals here (not sure where they come from) they have wiring diagrams you could use, but ideally you want factory manuals:
https://seccs.org/tech/1992%20SVX/
I ended up drawing up diagrams/maps of specific circuits, since they spanned many pages. Then I when through everything in the circuit, unplugging each device on the circuit one by one until something started working again. Then I plug things back in one by one to make sure I'm not dealing with multiple failures.
This work is a bit tedious, and you have to be meticulous about doing everything on the circuit, otherwise you're just relying on luck. A few times I've thought I was stumped, and that I had tested everything, only to recheck the wiring diagram and find some other things to check.
Maybe start with the tail light problem, that may be a simpler circuit. Check fuses, bulbs, and bulb holders (two bulb holders I had kept over heating and melting the plastic until I replaced them). Are your brakes lights working, are you reverse lights working, side markers, etc..
Good luck!
Ian.