I had a similar problem in my ‘03 WJ. After searching fuses and wire harness throughout, it chased down to the bulb holders. The heat from the bulbs over time cooked the plastic sockets to the point where they were so brittle they wouldn’t hold the bulbs securely, resulting in a very poor connection. I replaced the bulb holders and switched to cool running LED bulbs, which solved the problem. Check the bulb holders for heat damage, a burned appearance to the clip section that grips the bulb base. When I examined the old ones, the base clips in the bulb holder broke off like potato chips just from touching them.