It has been done.... but the ones I've seen they used the complete newer harness and everything electrical from the newer car. Do a search on dash swap or similar and you'll find several threads.
I have seen and participated in that swap being done.
BUT we were putting everything from the donor car (1992 GT) into the '86, motor, tranny, fuel tank, suspension, ect.
We used the '92 wiring.
I'm sure it can and has been done. But you would need the appropriate wiring diagrams and such to splice the correct wires into each other, not to mention the physical mounting of the newer dash requires some modifications to the '86.