Electrical help needed, underdash wiring is a disaster

What you found wasn't done just for the fun of it. We can only guess what was the reason. Once upon a time the turn signal switch failed, no turn signals, no brake lamps, or both. When someone replaced that switch they chopped out the OEM male and female harness connectors for the switch and made those wire up with butt connectors. Now the switch has failed again.
Instrument panel was removed to replace gauge voltage limiter, bulbs, whatever. Still doesn't work because the panel isn't screwed to the dash, it has no ground. They find one fuse marked [inst] has no power. Who knows what they might do to resolve what wasn't actually a fault.
So anyway... you may need a new turn signal switch whether you undo what they did or not.
Good luck with it.