'88 should have the one coil.
The coil gets 12volts when engine is cranking then 8 volts when engine is running, so there are two separate power paths for the coil.
Often on Fords the starter relay will have a 4th post, the "I" post, that connects to the coil and has 12volt only when cranking engine.
There should be another wire on the "+" coil post, it has a ballast resistor that reduces the 13volts(alternator) down to about 8 volts to keep coil from overheating.
This is the circuit you have a problem with.
Yes it could be in the ignition switch or at the ballast resistor.
If you have an ignition Module then Start and Run wires might both be there, and then to coil "+"
Good read here on the Ford TFI system:
http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml
If you run a jumper wire from coil "+" to battery "+" and then start engine it should stay running, this won't hurt the coil short term, so you can drive it this way, but you also should disconnect it so battery doesn't drain