I took them out to be tested and they both passed.  The volt meter reads the same @ the battery and alternator.  As well as the coil packs.  I never thought about the ECM.  I had no fault codes when I hooked up the tester.

The big tell will be the amp draw. That will point you in a direction but the computer may be the culprit since you said it happened all of a sudden. Just a guess though. Also make sure your starter is not stuck out and engaged on the fly wheel all the time. This happens rarely and the starter will still work like this but when the starter rotor continues turning after the motor is de-energized then weird things can happen. Use a multi meter and connect the leads backwards, + to - and - to +. If you don't have the same voltage (reversed of course) then you have a back feed. Everything I have said is all speculation of course but as with any trouble shooting you have to pick things off one at a time. Have you tried disconnecting the battery after the engne starts to see what happens? You can also try disconnecting the altenator and running on battery only with a battery charger connected to maintain the battery. This will also tell you if your system is overloaded somewhere.

Thats all I got. I'm an electrician not a motor mechanic but I have a little experience with the whacky world of automotive electrical systems and know how maddening they can be.

if you take a volt meter from the batt neg terminal to the eng block you should get almost zero volts any thing much larger indicates a poor ground in the system because the power of the battey is going through your meter to get back to the batt . these cars allso had a real problem with the power wire from the alt out terminal to the battery try a good size jumper wire from this terminal directly to the positive batt terminal and see if your batt voltage goes up .

Do voltage drop tests on power cables. You say the car has original cables?
Ford has molded plastic ends on the cables at the battery, at the starter solenoid, and at the power block.
These tend to corrode and break inside the plastic ends. This will show up with a voltage drop.
Good Luck.

Frist things first check all grounds to the engine and body. The 4.6 internally reg'd alt still requires a referrence from the ECM. So if you want, I can take a look at it July 1st if you like. I'm saddled doing electronic repairs most days, and it's usually a busted wire, bad ground, and rarely a failed part. Alternators and batteries do wear out, and you state you had em tested... Where and by whom? Test them elsewhere to confirm. I will look up the wiring at work today to see what where they go bad. I don't recall any serious issues with those cars.

Update, did you remove the factory dash/instrument panel? Because if you have, there is a wire to the field from it that is now missing.