They likely had the little filament in the sockey melt. It happens on a pretty regular basis in my 579. Pete sells replacments for $20 and they aint hard to replace at all. If your good with wireing snip the OEM ones out and put the ceramic ones in instead. The OEM ones suck and melt really easily if your plug gets warm but you havent pulled enough to pop the fuse. Also dont destroy the little black grommet. Pete only sells replacments with the entire pannel. Also when you do change them remimber to pull the fuses and also ensure the line is actully dead.