I'm presuming this is a 2-rail application, right? Driving an LED from from a varied AC or DC source is actually pretty easy, and there's no reason you should blow them up! Here's the circuit that is used in my passenger car lighting module, it's a constant current design that will take AC or DC and power one or many LED's, depending on how bright you want them. For a single LED, you could make an even simpler circuit to power it.
FWIW, I can't imagine how the sound system had anything to do with the headlight failure, that sounds like a real stretch! What is PFM sound, not familiar with that package?
