The large thick wires you found look like the blunt cut wires Ford provides for you to hook up stuff without cutting a hole in the firewall. You should be able to find these same wires under the dash near the steering column, just cut off or hooked to something if the previous owner used them.

You will have to clean off the wires really good and try to get the colors (near your finger in the picture) to have any hope of figuring out what the other plug is.