Hi,
I have been looking for options online as far as putting a sub in my 2003 V70. I am aware that volvo offers a package that costs $500-$600. My car is pre-wired for this but instead i have dedcided to go with the aftermarket option. i have built a box to hold the sub in place of the spare tire. I was just going to drop it in and plug it in until i realized what my car is pre-wired for is nothing like the standard subs are set up for. is there some kind of adapter i can buy? Do i need to upgrade my entire system? If and when it is installed can i control the gain from the dash? Please help me...

 

How are you planning to power the sub? You should be using a separate amplifier for it. You can add a sub and amp to your factory system by using an amp that accepts low level line inputs. In other words, it converts a set of speaker outputs from the factory system (take the rear speakers outputs for example) to inputs for the amp signal. There are some adapters out there that will convert the speaker outputs to RCA if you have an amp that does not accept low level inputs. As far as controlling the gain from the dash, a lot of mono sub amps will have a remote gain control that can be hooked to the amp to allow gain adjustment from the dash. Hope this helps.