I am having some ignition problems I can't seem to track down.  When I turn the key to the far right into the start position it will turn over.  I can even rev the engine.  But when I let go of the key it dies.  I replaced the ignition switch, key assemlby, and relay.
Any ideas?  

Chances are the problem is with the pink resistor wire under the dash. This wire goes from the ON position of the keyswitch to the coil and provides power when the key is in the ON position only.

To test this connect a wire to the positive battery lead to the positive side of the coil. When you start the car and release the key, the engine should stay running. If it does, you can replace the bad wire. DON'T leave the engine running very long with the wire connected to the battery and the coil, as you'll burn up the points in the distributor.

Let us know how your troubleshooting goes.  

I have a '85 Mustang GT 5.0 CFI. There are 4 black wires with green spots in a wiring harness that comes from firewall goes to coil, a/c, starter relay, etc. These 4 wires are soldered together with a blue fuselink. Where does this hook up to?  

I have a problem. Underhood on the right side,I have an extra set of 4 black wires that are soldered together and are not connected to anything. I'm not sure what they do either. Any ideas where they connect to.  

gclark:
Chances are the problem is with the pink resistor wire under the dash. This wire goes from the ON position of the keyswitch to the coil and provides power when the key is in the ON position only.

To test this connect a wire to the positive battery lead to the positive side of the coil. When you start the car and release the key, the engine should stay running. If it does, you can replace the bad wire. DON'T leave the engine running very long with the wire connected to the battery and the coil, as you'll burn up the points in the distributor.

Let us know how your troubleshooting goes.

Good advice Gary. The only difference between start and run is that pink resistor wire supplying the voltage to the coil +. There's also a bullet connection from the switch pink wire to the resistor wire that ties directly to terminal 16b of the 14401 wire block (which is the way the solenoid voltage gets to the coil). Time to go dash diving. good luck