Car Audio System Drwing too much power with 2...

I have a System in my trunk. Pretty Simple 1 Dual 8 ohm Voice Coil Sub(1000W RMS) with a 300 Wat RMS Amp. I idid this to make sure i nevver blow my sub. I have a FAT Plus Minus to battery, but all the sudden my amp would start kicking out at half volume. I looked in back and the protect light comes on at half power. So i bowwowed my sisters 1200 Watt Amp and hooked it up. I had it bridged off the amp both times. Anyways, Her amp worked great for a day, then i smelled smoke in my trunk. I felt her amp and it was pretty warm. Not her amp does the same thing? Is my car wiring bad or is it my sub or what? I had been using the same wiring setup for the last 3 years, so i cant imagine that would just go bad. Please let me know as soon as possible, I NEED BASS.