It is possible that the voltage regulator in the new alternator is not functioning properly and is not producing the correct amount when you have more load.
Test the alternator output to the battery with the engine at idle, both with and without the lights.
If there is fluctuation of the output, then the regulator is faulty.
Here is a helpful video and guide on how to test the alternator:
I have attached the alternator specifications below.
Please let me know if you have any questions.
Monday, March 7th, 2022 AT 9:28 AM