Where can you get a free radio wiring diagram for a 02 Ford ZX2?

Check with your local radio installing business such as Best Buy or someplace that offers free installation. If you ask them nicely most will allow you to view their charts, or are knowledgeable enough to answer any questions you can throw at them. Other than that, I'd say a local Ford Dealership's Parts Dept. should be able to find something for ya, or if you're lucky the service dept. will copy off the page or two from their factory electrical diagnostics booklet for your specific vehicle.