84 mustang premium power amp schematic model E3AF18B881-ED

Under hood fuse box , radio fuse 15 amp is what the factory service manual say's . Which radio does your truck have ?

Radio/Audio System Schematics (Base/Uplevel Radio - UQ3/UQ5)
Radio/Audio System Schematics (Premium Radio - UQ7 w/o Y91)
Radio/Audio System Schematics (Luxury Radio - UQ7 w/Y91)

What you are asking for are the design drawings, which are usually proprietary and not published by the designer.

Sans any definitive information, make, model, year... why you started wholesaling new parts... (none came thru).

You ought go back to the basics...

Fire, fuel & unrestricted exhaust...

On Board Diagnostics (OBD) might be pointing at several things...
You can also check manufacturer technical service bulletins for free on bbbind.com (plus good electrical schematic, below).

BBB Industries Premium Alternators Starters Power Steering Products

The 1984 model could be throttle body injected or a regular 4 barrel carb. The GT model is supposed to have a carb.
CFI is central fuel injection which is like TBI. The throttle body has two injectors mounted in the center, one for each bank.
If it has a carb you may have some adjustments you can make. If it is fuel injected you don't. The computer monitors the engine temp and exhaust gas to regulate fuel mixture.

http://t1.gstatic.com/images?q=tbn:HwNNXIQY8islbM:http://www.allfordmustangs.com/forums/attachments/classic-talk/85491d1260574424-how-install-wooden-steering-wheel-1966-mustang-steering-wheel-break-down-sheet.jpg&t=1

http://media.photobucket.com/image/1984%20mustang%20steering%20column/jwko/0900c1528004bb08.gif


http://www.shbox.com/1/steering_column_exploded.jpg Not sure if this is a mustang one

Only if it is fuel injected !!

You could do turbo or supercharge. On a '84, you should be able to find a wrecked/donor v8 model and do a swap. You will need to exchange many parts but you would have them.

go to your local junk yard, plenty of must to choose, the parts at half price

jumper the low pressure switch on the Acc. if the AC runs, check the charge on the A/C if the charge is correct. replace the LPS.