it depends on the needs of the subwoofer.
Yes it can power the sub.
there are lots of reasons to not use the factory wiring
greatest is the possibility of wrecking the sub because of low power to it.
You would be much safer and you would be happier with better sound if you run new signal wires to a new amp using an adjustable line voltage converter.
it takes your head unit voltage and you adjust up or down untill you get the correct voltage for the new amp.
It wires into your speaker out of the HU and converts that to RCA jacks out of the converter, than its RCA and a turn on wire back to the amp. Put in a couple of splitters before the amp if you want to run 4 chanels.
I would get a 4 chanel amp and run the rear speakers off of it also. Not to bad to do once you are there.
You can get some Boston coaxals 5 1/4 into the space behind the seats with some enlarging of the stock speaker openings, for like 50 or 60 bucks a pair.
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