These might help a bit:
thats from my 83. Basically, all it takes from the car is 12+, 12v acc, illumination signal and ground. Earlier models could also come with a clock that only had power and ground, but those are very early foxes.
the clock in the console of a fox mustang is largely self contained. All it takes from the car is 12v power. As far as “electronics” go, these little units are pretty basic, not much to go wrong. If you don’t find a burnt resistor or leaking cap, its probably cheaper to find another in the scrap yard and just swap it out. They’re not too expensive, I’ve got 3 or 4 in a parts drawer somewhere and probably another 2-4 still in their consoles up in the rafters.
The drivers message center is a different story. It uses sensors out in the cars wiring harness for info. For example: fuel level is handled by a summing unit behind the passenger dash panel. The “light out” actually looks for a specific resistance and the car needs the harness for the lighting with special resistors out in the harness in various places. Its PITA to swap a console into a non-console car, mainly from just chasing down the wiring. When I swap in a console, I make sure I pull the dash and lighting harness from the donor car. Last one I swapped in I just unbolted the entire dash and walked away with it. Much easier to just swap the dash plastic with the needed sensors and wiring already installed.
if your buddies mustang is in decent shape, tell him to hold on to it. Early foxes (302/5L) are starting to go for good money. Its not uncommon here to see clean axamples asking anywhere fron 25-50g, depending on option level and condition. The Fox chassis is experiencing what every “performance” car eventually does: the guys who couldn’t afford them when they were new now have money and want to scratch that item off their bucket list…and they are willing to pay for it.
last year, I actually had a guy offer 25G for my 83. It has t-top, 302, 4bbl, 5 speed, etc and its still a ”non-running” project car. You tag the right guy and they are willing to pay pretty decent money for them. they’re not exactly “rare” (ford pumped out a gazillion of them), but the earlier “4-eye” foxes are getting harder and harder to find in GT and good, unmolested condition.