Amp Blows audio fuse 1995

[jokerboy]

I have a 1995 Nissan Pathfinder, Just got it. The 10a audio amp fuse kept blowing. I pulled the 2 amps in the back passenger side. I put a new fuse in it did not blow. I plugged the amps back in. It did not blow but also not work. I touched them to body to ground, I got sound (rear speakers only). I reinstalled the front amp(by frnt I mean closer to the frunt but still in the rear of the car), fuse blew. I took it out and unplugged it. I tried it with the back amp out but grounded, sound. I reinstalled the back amp. Fuse blew. I took out the rear and tried again with it grounded but not mounted. Music. I ran a ground wire to the amp and just stuck it in the rear well. It works. Why are the fuses blowing when the amps are intstalled (which really is just mounted). But not when they aren't?????

Thanks,
JB