The answer to 'why is my junction box dimming lights' is that a problem with the junction box or its connections is causing voltage drops that make the lights dim. This could be due to loose or corroded connections, overloaded circuits, or issues with the wiring inside the junction box.
Symptoms of a dimming junction box include lights that flicker, dim, or pulsate. This can happen when you turn on other high-wattage appliances or devices on the same circuit. It's important to address the issue promptly, as dimming lights can be a fire hazard. If you're not comfortable troubleshooting the junction box yourself, it's best to call a licensed electrician to diagnose and repair the problem.