My friend has an 87 Ranger and the engine will only run while the starter is being cranked. As soon as the key is let go the engine stops. What's going on here

 

start with the basics - is it getting fuel and is it getting fire?

 

Is the engine actually firing over when the starter is engaged? Can you tell it's kicking over, but only 1 or 2 cylinders are firing, so the motor can't sustain itself? Will it run on starting fluid? If so, then you've got a fuel issue. If still nothing, or the same symptoms, more likely a spark problem.

 

ign switch failure---disconnect switch, power to coil or control box, jump solinoid

 

I can jump the solenoid but where on the control box do you connect power. The engine runs good as long as the starter is turning

 

I can tell you with 99% accurracy that the TFI is faulty.
Here's the reason why.
During starting, the ignition switch supplies power to a seperate input on the TFI.
When the key is let up to run, the ignition switch transfers over to a second power lead to the TFI. It is this circuit that has the fault for a no run after crank.
I have saw this before and proved the fault by crossing these leads and allowing the engine to start and run. The removing of the cross the sees the same fault again. New TFI cleared the problem.