Couple things.....
Mark,
I just went through a similar set of 'gremlins' on my 89.....
This is going to sound weird..... Check to see if your backup lights are turning on when you put it in reverse. The reason is that the turn signals and the backup lights are on the same fuse. I had a fuse that looked good, smelled good, tasted good and checked good with an ohmmeter, but when put in the car.... wasn't good! New 10A fuse fixed the blinker problem. I now have 2 'spare' blinker modules....
The other problems took a little more time..... There are 3 wiring harnesses that run under the carpet on the driver's side of the interior. FORD saw fit to put in numerous splices in all three of the harnesses. Actually not a bad place, mostly protected, not much moisture or chance of damage, etc....
HOWEVER.... I found a bunch of them either broken from corrosioon or I just felt I should redo any and all splices I could find in those harnesses.
This will take a few hours, since I had to remove the driver's front seat, and kick panel to gain adequate access to the harnesses. You will also need a lot of crimp connectors, or be a whole lot better with a soldering iron than me. Get and assortment of sizes, since FORD put 4-6 wires into a single splice, the guage adds up quickly. Yellow blue and pink, all have their place.
I used 'plug' and 'receptacle' type so I could repair things if need be.
It sounds silly, but I also went around the car and CLEANED all the grounding points, they look like harness connectors that just end in a bolt.
Two just inboard of the headlights in front, one under each kick panel inside the car, one on the passenger side of the trunk, buried under all the carpet above the fenderwell. There is supposed to be another one behind the glovebox, for the engine computer, but I haven't taken the glovebox apart yet.
Doing all this fixed probably 15 different things that were either acting weird or just not working on my SC. Everything from flashing idiot lights to non working courtesy lights, to keyless entry, just all started working again.
I also checked the passenger side harnesses but couldn't find any splices in them. Should save you some time, not having to remove the passenger seat too.
Hope this helps!!
Lance