another posible thing is it could be a bad fuse. ive had two bad fuses the glass tube looking ones which are typical. even tho the fuse wasnt blown apparently the solder on the end must have been cracked or something and sometimes it just wouldnt let power flow to the amp and sometimes it would work just fine. was a REAL PITA to figure out! but with a simple light tester it can be found if your amp keeps going out.
and like some people already said also check the wires for the subs, check to make sure there is no loose wire strands that could cross onto the other terminal on both inside and outside of the box and also on the subwoofers themselves. of course it could also be bad terminals on the subwoofer box cause ive had those before go bad, which is why i dont use those cheap ass sub box terminal caps! its easier to either drill a hole in the box and just stick the whole wire thru it and seal the opening so its a one piece wire and still sealing the box. another way to go cheap is with two holes you drill in the box and 2 bolts and four nuts and then just use a washer or silicone and use the bolt as a terminal. simple ring terminal on the inside of the box with the bolt sticking out of the box and tighten a nut on the back to make it solid to the box, and then just use the second nut with another ring terminal for the wire from the amplifier. very simple and cheap! no weak pieces of plastic to break and fail.
just keep fiddling around and testing things. a simple light tester and a ohm meter will find most problems!
