Q: Issues with the lights flcikering

I purchased this pre-owned car and I've been having some issues with the electrical system. There is some flickering and dimming of lights. This happens both outside and inside. I took it to a shop and they had the alternator wire rerouted, so that there would be no interfering. The problem remained the same. Then, they had the alternator replaced as there were high-pitched whining sounds when it was under load. I thought that would solve the issue but it didn't. It did change something however. Instead of flickering, the lights pulsate. What should I do? Thanks.