your test light shows positive voltage on both coil wires on the pickup because it has pos on one side, then through the coil, and pos coming back out...I'm betting your test light showed pos voltage only on one wire on the running bronco...the other wire was grounded on the bronco, but on the f series it is not....
the coil has a constant pos wire, and the ground is switched through the ignition control box, which is a common part to fail (common enough to keep a spare one in the glove box) of course, your test with a test light does not prove anything, since the ground is switched on and off, so a good working system will show pos at both wires at different times....connect your test light between the ground terminal at the coil and battery positive and see if it flashes when the engine is cranked, do this while everything is connected properly. If it does not, then connect the test light between the coil pos and battery ground, and repeat...if the test light goes out at all during that test, then check the constant pos wire. If the pos feed to the coil is fine, but no flash is seen on the ground side, then suspect the ignition module or wiring, pay close attention to the connector at the ignition box, known to corode/possibly melt
since you just swapped motors, I would first double check all wiring connections, especially grounds..you could also try hooking a jumper cable between the battery neg and teh engine block to verify that it is properly grounded