I own a 2003 Enthusiast coupe. I opted for the non-bose system becasue eventually I will replace the head unit. The base system sounds great imo. I just want to add a sub and small amp. Can this be done with the stock harnessing? Or do I have to wire in the sub/amp myself?

 

no and yes

 

You will need an amp with high level (or speaker level) inputs. You will need to splice the speaker wires to feed the audio signal to the amplifier. If your amp does not have said inputs, you will need a line-out-converter which converts speaker level signals to pre-amp level signals.

 

the amp I am using has high level inputs. I am not sure if non-bose Z's have any wiring there at all to do that with tho. If there is a harness located in that sub box behind the driver's seat this should be easy.

 

^^^^ there is not. You can tap off the wires feeding the rear speakers.

 

I got a line out converter and spliced it into my rear speakers before I got the D3. I would advise against it, because it sounds like crap! You have to fade it weird and overadjust the bass on the head unit resulting in muddy highs.