I have a 1991 d250 Cummins. Just recently started noticing a terrible smell inside the cab coming from the vents. Especially when the AC or heat is on. Under the hood it kinda smells like it's coming from my battery. It's almost like a cross between burning plastic and boiled eggs. Any ideas? Also when I was messing around with my radio I happen to creat a little spark and now my radio does not work nor do my interior cab lights work. From some reading it's the I.O.D fuse but I absolutely cannot find it. Any help with that?