Wiring a sub to the factory HU
 

I got my sub installed at a local shop and they connected it to my HU in an odd way. There's no subwoofer control, and after playing with balance/fade controls, it seems like they spliced it into the front left channel. Is there any benefit or drawback to having it wired this way? It's going to a separate amp with a low pass filter, so I'm not getting upper frequencies seeping in and everything sounds just fine. I just don't have separate sub control (other than the amp itself). Curious if that matters and if I should say anything when I eventually get a nav HU installed later on?

The factory FRS base stereo has SW preamp outputs you can turn on. Should have used those instead.

Just cut what they did off, and run a set of rca's. It's pretty easy and wont cost more then 15-25$.

It's just strange because I've had nothing but good luck with this place for some time and it looks like the guys know their stuff. Any reason why they would install like that instead of using the subwoofer plugs?

They prolly assumed being oem that it had none.

Maybe they did a BRZ before? No subwoofer out on them so they may have assumed not to even bother checking the headunit.

I would definitely take advantage of the preamp output you have. Although I'm not sure if you'll really notice a difference as it'll be hard to hear cleaner low frequencies.

no excuse for only using the left channel.

Not wasting my time with it this time around because I plan on upgrading to a nav unit soon (likely Pioneer X950BH or X850BT). I'll make sure to mention it then. As of now, the sub still sounds pretty clean, provided I have a clean audio file and the trunk isn't too rattly.

Bummer, altho, the amp already has power ran to it and its connected to your sub already. The majority of the labor is done. All u gotta do is get a set of RCAs and get access to the back of the deck and run them under the carpet to your amp and plug them in. Of all the things they could have f'd up, this is a pretty easy fix if u want to DIY.

On the other hand, if my stereo shop made this error I would find out who my installer was and talk to the shop manager and show him the work that was done. Chances are it was installed by the shop intern and its important that they get trained properly so I would bring it up with the bossman.