kenwood 9152d Mono amp clipping?

This may seem a stange thing to check, but the Kenwood is a mono block and the + and - speaker outputs are not side by side, maybe you got the two + wire to speaker.  We run 3 12" of the amps with no problem. 

You say you get 11.8 volt at the amp.  This seems low, and on a bass hit it may drop below voltage shutdown.  Does the amp run hot?  You say the amp is clipping, but if the amp shuts down and comes back on after a few seconds, its not clipping, but protecting itself.  Check that the ground is short, and good solid contact to body/frame.  Also, check the fuse, we've had more than a few (AGU) that look good, but don't pass much voltage/current.  Get your voltage up over 12.5 at the amp.