fuse blows in reverse

I noticed my backup lights weren't working, so I changed them out. I know, should have checked the fuse, which was blown by the way. I replaced it, but as soon as I put it in reverse, it blew again. I took the rear light off again and I didn't noticed any pinched wires or bad places in the insulation that I could see. I replaced the fuse one more time, it blew again. Needless to say, I have no clue why. I have not messed around with the electrical system lately. The last time I did was when I added some subs and an amp, but that was a while ago.

Has anyone ever ran into this or heard of it. Do you have any suggestions?

I'd hate to take it to a dealer to do an electronics check on it. The last time I did that with a vehicle, 1997 Isuzu Rodeo, they told me what all wasn't wrong, but couldn't find what was. On top of that, they said that they do not check for shorts in the wiring. Maybe it's just me, but what the hell kind of good can an electrical system check be if they don't check for shorts?
 
well sounds like you have a short somewhere. you will just have to troubleshoot it most likely.

make sure you check the whole path. switch and all. there is more wiring to that cicuit than just at the tailight.