Ok, you have an '87 Turbo with a '91 Turbo wire harness... I vote either something's hooked up incorrectly or you have a funked up relay...
I know this isn't quite the same, but a headlamp relay in my Solara went bad (it was actually an aftermarket one, I was going for HIDs)... Whenever I put both my turn signal on and my rear window defrost on my car would stall out completely, even in motion... It was really weird... If I had my headlamps on and put EITHER the turn signal OR the rear defrost on, the drivers side light would dim completely off... When I put them both on at the same time, the car would simply turn off...
So check your wiring thoroughly, and check your headlamp relays... Either way, you can get some trippy stuff going on if something's not right!!!
Good luck,
-James
Whacky stuff...