The answer to 'why is my junction box burning smell' is that a burning smell coming from an electrical junction box is a serious issue that requires immediate attention. This could be caused by overheated or damaged wiring, a short circuit, or an electrical fire inside the box.
Some common symptoms include a burning smell, sparks, flickering lights, or warm/hot junction box. This is a fire hazard and should not be ignored. If you notice any of these signs, turn off power to the circuit immediately and do not attempt to open the junction box. Call a licensed electrician right away to diagnose and repair the issue.