Where is the voltage regulator - 1994 Ford F350 Crew Cab

A voltage regulator is just that. You need an auto electrician to diagnose the fault. It is a lot cheaper than the dealership.

https://www.google.com/search?q=mobile+auto+electrician+near+me

The Voltage Regular is part of the alternator, so it is not a smart module that phones home and asks questions.

https://www.google.com/search?q=voltage+regulator+for+a+Porsche+Cayenne

..

If I'm not mistaken, GM has had the voltage regulator internal to the alternator for years before '93.
The alternator has to be disassembled to repair the voltage regulator. Most do-it-yourselfers just replace the alternator.
Here's a picture that shows the regulator at RockAuto -

1993 CADILLAC ELDORADO 4 9L V8 Voltage Regulator RockAuto

Around 15 + or - a little. This indicates the alternator is charging.

Hello, again, again Bridget. First I sent you explanation of the ignition system and I gave you my best guess---ignition module on your 1994 Plymouth with V6 3.4 L engine.

As far as voltage regulation goes there isn't any external devise to do this. This voltage voltage regulation take place inside the alternator after the three phase AC voltage is turn into none regulated DC voltage. Now this DC voltage goes thru a voltage regulator that built into the alternator where the output DC voltage is 13.8 to 14.1 DC Volts. Now, the alternator is regulated for current by the it wire windings in the alternator. Larger the copper wire the more current the alternator will produce. GB.....stewbison

It sounds like you have done a whole lot of replacing and not much "diagnosing". Did you chech for battery voltage at the alternator? There should be battey voltage at the large Black/Orange wire that is on the B+ terminal of the alternator. This wire should have voltage all the time. If there is no battery voltage, you most likely have a burned fusible link at the starter relay area.
There should also be voltage at the "S" terminal with the ignition on. If there is no voltage, then check for voltage at the "S" terminal of the voltage regulator. If there is no voltage at the "S" terminal on the voltage regulator then check the "I" terminal on the regulator for voltage.

NOTE: The voltage on the "S" terminal should be 1/2 that of the voltage on the "I" terminal.

If there is voltage on the "I" terminal, make sure your voltage regulator is grounded properly to the fender and retest to see if it is charging the battery. If it is still not charging, disconnect the regulator connector and connect a jumper between the "A" and "F" terminals of the connector. Start the engine. The alternator should now be charging the battery at high voltage (usually over 15 volts) If it does, replace your voltage regulator. If it does not, then you need to check your wiring between the voltage regulator and the alternator.

Please also review this article:

What Else Could Be Wrong?

VOLTAGE REGULATOR IS LOCATED BEHIND BATTERY.YOU PROBABLY MIGHT HAVE TO REMOVE BATTERY TO REMOVE THE VOLTAGE REGULATOR.

Wiring Diagram for that voltage regulator

The voltage regulator is inside of the alternator, it is an integral voltage regulator, so if the voltage regulator is faulty, the whole alternator needs to be replaced.

The voltage regulator is probably in the alternator. I don't think nowdays you can buy voltage regulator separate. If the voltage regulator is bad, you'll need to buy an alternator.

The Voltage regulator is in the PCM.