2004 Tribute Sub/Amp

:
2013 CX-9 Grand Touring
Got a question about wiring for the sub/amp.

I replaced the factory head unit because the CD player and lcd readout both quit working. I bought the Metra wiring harness so I didn't have to cut/splice. There are some wires not used: dimmer, power antenna +, power antenna -. I used the amplifier + to connect to the new head unit amp +12v wire. Problem is the sub has no sound. Not sure if there is no power to it, possibly it needs the negative wire hooked up.
Does anybody know for sure if it is a positive or negative trigger wire that is needed?

Thanks!
 
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