The turn signal issue may be at the hazard switch, but you are correct, the white/black wire is the thick wire from the fuse. Unpin it from the switch and check to see if it is still shorted. I think you did pinch the wire somewhere re-assembling the dash. The 91 is a bit different from the 90 I show in the dash pictorial (emphasize these things I write are not instructions) and there are some photos of the 91 in my heater core replacement description.

My bet is on the wire, as part of the loom across the lower dash, got pinched and there's either a screw run through it or it is just squashed in the framework near a fastening point. Good thing it had a fuse in it, huh?
--
Art Benstein near Baltimore

They say you can do anything in international waters.
That's why I filled my hot tub with international water.