99 Ford Explorer radio display doesn't work - how do I fix it?

[itliketbeef]

I have a 99 Ford Explorer with factory premium sound (steering wheel controls, 6 disc changer and rear controls.) The radio works great but my problem is that the display doesn't work. I know this is a common problem; I bought a used radio but it also has the same problem. How do I determine that the issue is with the radios and not in the wiring harness? There are a lot of wires in the harness, does anyone know which one controls the display? I do not want to switch to an aftermarket radio and I don't want to spend a ton of money to purchase the wire diagrams. Any help would be greatly appreciated!