Welcome to 2CarPros.
Honestly, I think you are heading in the right direction. If the lights are dimming before it happens, either the alternator isn't working correctly or there is a bad connection.
What I want you to do is simply perform a basic alternator test. You will check battery voltage with the engine off and all components off. Then you will check battery voltage when you start the engine.
With the engine off, you should see right around 12 volts. With it running, it should be around 14 volts. In addition the alternator needs to be able to maintain under a load, Follow the next link for testing.
Here is a link that shows how it is done:
https://www.2carpros.com/articles/how-to-check-a-car-alternator
Here are a few other links that you may find helpful:
https://www.2carpros.com/articles/how-to-use-a-voltmeter
https://www.2carpros.com/articles/how-to-check-wiring
Let me know the results or if you have other questions. Also, make sure the battery terminals are clean and tight. Corrosion can cause problems, too.
Take care and I'll watch for your reply.
Joe
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Monday, March 11th, 2019 AT 6:42 PM