I just cleared my messages to make more room.
If your replacement '90 unit came from a car with the factory CD player, it will be virtually silent without a working CD player attached, even from radio & tape. Ford made Premium Sound head units that were to be interfaced with CD Players, and those that were meant to work without the factory CD. The only way to tell them apart is by their part number. That MAY be your problem, but, these particular units are so troublesome until rebuilt that both could have issues. They ALL fail in time due to leaking capacitors.
I am still around but I'm taking about a much needed 6 month break from my repairs that I have been doing for the last 15 years.
If you can wait until the first of the year, reach out to me at email@example.com