Hmm.. maybe I read this a bit wrong..
#1 = Wiggle the sub, and it kicked back on= possibly loose connection
#2 =Ground wire hot burning seat= poor ground/too small of ground supply needed for amp
#3 = Checking Ohm oad with DMM,and all over the place?= No reading /bad reading, Blown sub??/Should read close to Coil ohm load a bit higher,or lower..not moving..
#4 = Put sub in buddys car not knowing what ohm load you are at?= Could have been at a lower ohm load than his amp could handle,and fry his? I would have told you go fvck yourself on that one
#5 =New sub,new box not working on existing system either?= No supply/power to sub,RCAs not hooked up,Blown fuse on amp,wiring issue on amp,HU settings not correctly set for sub amp...FRIED AMP
About all I can think of without more details of even if amp powers up at all/LED indicator working or not ect.
#6What could be wrong?