Fuse box question

[TheCougarine]

So I've got a question for any of you electrical experts out there. I have my amps remote power wire wired into the factory radio slot on the fuse box so that it will turn off and on with the switch. This has been working perfectly for over 6 months. Today when I shut the truck off, the amp stayed on and I had to unplug it from the fuse panel to turn it off. I didn't really have much time today to really look into it but I wanted to see if anyone on here had any guesses about the situation. It seems like the fuse is now staying hot even with the ignition off. Could it be the fuse its self? A grounding issue? A short of some kind? A little direction would be a massive help. Its a 71 GMC btw and thanks in advance.