Same here, im told its because the woofer leads (red and black wires) need an adapter to use the sub woofer with an after market stereo. got me one of them disco woofer adapter leads off ebay but can only plug in one end, then theres nowhere again for the adapter to go. I asked the guy in my local car audio place what does he make of it , he replies "ah sure I wouldnt bother with that yoke"
"That yoke" beats the hell out of that piece of crap kangoo he got outside the shop
anyways i think the amp needs to be powerd aswell as plugging in the woofer leads but then again I dont have a clue iether