not sure i totally understand the concern, but it sounds as tho the ignition switch is faulty.
first it would be a good idea to check the battery to body ground and the battery to egine ground wires.
as well as checking the condition of the positive wire to the starter relay wires, also check for burned fuse links near the starter relay if there are any.
get a good test lamp, not the cheezie $2.00 kind, you'll need something that draws a few amps, like a headlamp bulb.
make sure the test lamp works, and look at the brightness of the bulb.
disconnect the red/blue wire from the starter solenoid.
while leaving a good ground from the testlamp, (suggest battery ground cable) point the testlamp toward the driver door so you can see the light, hook the other end of the testlamp to the red/blue wire.
turn the ign key to start, if the light glows as brightly as it did hooked up to the battery, then you will have verified the starting system circuitry from the ignition switch to the starter relay is serviceable.
if the light does not glow, or is very dim, you may suspect a faulty ignition switch, wich can be tested fairly easily by removing the steering collumn trim, and testing for voltage at the red/blue wire while the ignition switch is in the start position.
it is a common concern with this type of ignition switch fitted to the older vehicle to have the the switch housing become seperated from the plastic base, (in fact there was a recall on the thunderbirds years ago).
if there is no voltage at the red with a blue wire, reconnect the red/blue wire to the starter relay, and if you like, you may choose to use a fused jumper wire rated at 15 amps or so, and short one of the yellow constant live wires at the switch to the red / blue wire, and see if the relay operates. if the relay operates replace the switch.
if the switch is bad, i suggest replacing it with a ford one, as most of the time they are cheaper and are more reliable than napa or the others.
i hope i havent put you to sleep with all this writing, but i hope it helps.