The car has been Idling rough and stalls now and then. Pulled the coil wire off and touched it to ground and turned the key on. The spark is yellowish orange. Most of the info I find says the spark should be blue. Does this sound like a bad coil?
I had only one problem with 5.0 Fox Mustang ignition coils, and it was very difficult to diagnose. The car would only start intermittently, and ran poorly when it did start. Since the EFI ignition coils were cheaper at that time, I now have a spare to swap.
The cost of a replacement coil for your car looks to be in the $18-$28 range, so if you can get one from the junk yard it might be much cheaper.
Prior to replacing the coil, do some simple checks like making sure all the electrical wiring is in good shape and the connections are clean and not loose or corroded.
If I am not mistaken, you car came with a DuraSpark system. Here's a diagram for it...
Duraspark II ignition diagram: