Fifth Wheel Wiring Issue?

Alright, I'm hoping I can get some help here.. I recently purchased a 1983 royal coachmen camper.. I've been in the process of fixing it up. yesterday I decided to put a radio in it, it is already wired for one. So I went out and bought a cd player from walmart for a car, tested the wires in the camper, one had power the other was a ground with some speaker wires, I hooked it up and it would try to eject the cd but wouldnt turn on, it also blew the fuse, I put a bigger fuse in the cd player (stupid) and it did flicker on once, I was getting quite annoyed at this point and somehow manage to switch the ground and power wire around and it fried that cd player. So I bought another one today, hooked it up and the cd player just made a buzzing noise, wouldnt turn on.. i left it hooked up to power and after a minute it blew up in my hand.. with a crazy amount of smoke.. never blew the fuse or anything.. it looked like the previous owner had a car cd player in it.. So i'm trying to figure out what i'm doing wrong here? or if it could be a wiring issue with the camper? I've already wasted $300 and getting pretty frustrated with it... Thank you for any help!