The only thing that regulates voltage is the regulator and it is internal. Since it is overcharging, chances are that is the problem. Based on your description, it sounds like it needs replaced.
If you want to check alternator output, here is a link that explains how it's done. You could check it at idle and when revving the engine to confirm it is overcharging.
Here is a link that explains in general how one is replaced:
Here are the directions specific to your vehicle. The attached pictures correlate with the directions.
Before starting, make sure the battery is disconnected.
2003 Ford Crown Victoria V8-4.6L CNG SOHC VIN 9
Vehicle Starting and Charging Charging System Alternator Service and Repair Procedures
1. Disconnect the battery.
2. Remove the screws and the engine cover.
3. Loosen the clamp and remove the intake induction resonator.
4. Release the tension and remove the accessory drive belt from the generator pulley.
5. Remove the nut and disconnect the generator electrical connectors.
Position the cover aside.
6. Remove the bolts and the generator bracket.
7. Loosen the bolts and remove the generator.
1. To install, reverse the removal procedure.
Let me know if this helps or if you have other questions.
Images (Click to enlarge)
Wednesday, August 12th, 2020 AT 9:05 PM