Couple of different ways to go about this Harold, depending on how much you feel like doing your own wiring. I have some factory wiring schematics if you need copies, feel free to send a PM.

I had a blue '88 T/C with a 5.0L Vortech, 5 speed a long, long time ago and have messed with a few others since.

1) You can contact the guy that used to run Windsor Fox for a custom built, plug and play 5.0L EFI conversion harness into the '88 Turbocoupe, that uses all the correct Ford type plug-ins and connections. You'll obviously have to specify whether you want S/D or Mass Air and if the car will be AOD or manual trans. I'm not sure on pricing, I'll try to see if I can find his contact info somewhere because I think he retired and closed down Windsor Fox.

2) You can get the wiring pinout diagrams for both, your Turbo Coupe and whatever year mass air or speed density harness you have, and do the required repinning and some splicing and soldering to build your own 5.0L EFI conversion harness.

3) If you are okay with Speed Density, you can either repin the TurboCoupes chassis harnesses to interface properly with a 87-8 5.0L T-Bird's harness. Or you can reharness the entire car from headlight to tailight with the 87-8 5.0L T-Bird's wiring, assuming you can find a complete uncut one in the junkyard.

Keep in mind that Ford changed harness plugs/connections/grounds/relay locations on Fox Thundebirds every single year. Also keep in mind that the '87-8 Thunderbirds had 3 different engine offerings,4,6,8 cyls, each with their own unique engine and chassis wiring harnesses. Third, keep in mind that these year Thunderbirds also had various trim and option levels that further complicates and hinders easy plug-in engine to chassis, or even chassis to chassis, wiring harness compatibility.

All of this to say that Fox T-Birds are not quite as simple to properly and cleanly convert from 4cyl EFI to 5.0L EFI as Fox Mustangs are. Have fun.