Electrical troubles

Your issue seems to be related to your car's charging system, particularly the alternator, battery, and associated wiring. If your car's voltage is dropping while the engine is running, it's likely the alternator isn't charging the battery effectively, which could explain the battery light flashing and the P0622 code (Generator Field "F" Control Circuit Malfunction).

The corrosion on the wire you mentioned could indeed be a factor. Corrosion can impede the flow of electricity, leading to insufficient charging of the battery.

Before taking it to a shop, you could consider the following steps:

1. Check the Alternator: Even though you replaced it recently, it could be faulty or not functioning properly. If possible, you can have it tested to confirm it's working as it should.

2. Inspect the Wiring: Corrosion, fraying, or breaks in the wires leading to/from the alternator and battery can cause issues with the charging system. Pay close attention to the wire you mentioned, as well as others in the system.

3. Check Battery Connections: Ensure that the battery terminals are clean and the connections are tight. Loose or dirty connections can cause charging problems.

4. Examine the Serpentine Belt: This belt drives the alternator. If it's loose, worn, or damaged, it might not be turning the alternator effectively.

5. Check the Ground Connections: Poor ground connections can cause electrical issues. Make sure all grounding points are clean and secure.

If you're not comfortable with these checks or the problem persists, taking your Evo to a professional for a proper diagnosis is a good course of action. It's always better to spend a bit on diagnostics rather than replacing parts that may not need to be replaced.