It's very simple. You just wire up the Toyota stereo harness to your head unit and hook everything up just like the stock head unit was. I've had a Kenwood DNX7100 wired up that way for over a year and it works perfectly. You won't have the same kind of control over the sub that you would if it was a custom amp+sub setup, but it works the same way as it did with the stock head unit.

 

Ahh I cant remember how does the back of my DDX-512 unit look. So I wont need to splice anything?

Kinda confuse because the OEM sub has a plug that goes into the OEM head unit right?? Where would I plug that?

 

The OEM sub harness plug in between the head unit and the car harness. Once you have the same Scion/Toyota harness wired to your head unit you plug that into the sub harness which then plugs into the car harness.

 

I don't suppose you can elaborate a little more on this JasonH? Would something like this work if i wanted to get a new headunit (like this one http://www.amazon.com/Pioneer-AVH-P3...=1XYURZYYFF7GI) would this allow me to use my stock sub (http://www.amazon.com/Stereo-Harness...=1XYURZYYFF7GI) ?

 

Yes, exactly. You just wire the Toyota/Scion harness to your new head unit and it plugs into the car (including the subwoofer) just like the stock head unit.

 

Awesome, thanks man, further proof that Jason's are awesome.

 

i might be the first one to state this: but you have ADD on installing the sub. you start with somethig else, and you start installing the sub, and then u jump to cabin filter, and you jump to a little about the sub, and then you jump to interior lighting....

this is kind of hard to keep up

 

I took pictures as I went throughout the process and wrote the how-to accordingly. If it didn't help you out, so be it. If you have questions I can probably answer them (as you may have seen elsewhere in this thread.) I know the how-to has been helpful to plenty of other people.