V*R*6

ok so i know nothing about setting up systems, but here goes...
i recently bought a car and put my amp and subs (which worked perfectly fine in my old car) into the new one, that was already wired up.....i connected everything, but my subwoofer runs for 15 seconds at best, and then cuts out....my buddy tested the voltage and everything is getting power.....is this something to do with the deck? or maybe not the wire isnt a thick enough gauge? any help would be appreciated...