Silly question but....using WRX under-seat sub in the BRZ?
 

My buddy is in the process of upgrading his audio system in his 2013 WRX.

He was trying to decide what to do with his current factory under-seat sub, and offered it to me for my BRZ.

Can it be hooked up to the stock BRZ HU, either with the factory harness or by doing a little work to it?

Apologies if this has been asked before, I did a search and couldn't find anything.

would it even fit? I have to pump my seat up just to fit my hand under there

I'd be willing to relocate it a little, have it right up against the footwell in the back seat, I'm just more curious if I can wire it into the HU without needing to do anything fancy.

The factory under seat subwoofer has a T-harness that splits the signal from the headunit down to under the seat. If your friend still has the entire T-harness, make sure he gives that to you so you can do the next part: cut off the headunit side of the plug. It likely won't fit the stock headunit plug. Then you get to figure out which wire goes to L/R speaker +, L/R speaker -, 12V power, and ground. Find the corresponding outputs for these connections from your headunit harness and use a vampire tap or something like ae64's headunit wiring harness.

The subwoofer, which is actually just a 6.5" woofer with a high-pass filter, isn't all that great. I had one in my old car and it was terrible. Got rid of it for a real subwoofer about a week later (that's how long it took me to collect parts).

For the amount of time and effort it would take to make it fit you could just install a decent trunk setup.

Thanks for the responses. The main reason I was thinking about it is because it'll be free. I'm really not interested in spending money on anything audio related at the moment, but if I can do anything to improve the stock sound for cheap (read: nothing), I figure I should at least look into it.