Stereo amp installation issue

I had an aftermarket radio and an amp and subs all in my vehicle working fine but decided to upgrade with a better amp. Prior to doing this I had put new terminals and new wires to my battery. Just one of the extension kits you get at any auto parts store. So now as soon as I got done running everything I was ready to connect the hot wire to my battery that supplied my capacitor and amp. My radio was already installed and working fine. As soon as I touched the hot to the battery I look and smoke comes pouring from inside. I couldn't figure out what happened but the ground wire was burnt. Ground to my radio. So I decided to run separate lines from the battery and fuse box and use a new ground source. Found a bolt under dash that worked for the ground. So I have the radio up and playing and I run all new wires to everything. Again, soon as I connect the amp hot wire to battery, smoke everywhere. It was the ground wire again burnt. And this was the one I just ran myself. What is going on here? Did I cross a wire to my battery or something? Can't figure it out and blew up 2 $300.00 radios already. Please help