I like the factory Sony system that came with my Focus ST, but wanted to get a little more bass. This APSUB allowed me to piggyback off of the factory stereo with plug and play harness to a new amp. Factory amp was retained for all of the other features I didn’t want affected. Swapped the 8 inch sub out for a new one that I retrofitted into the factory box. Hooked it up to the new amp and man what a difference. The APSUB even provided a gain knob I added right under my e-brake for ability to control bass level from the drivers seat. Great product and works really well with factory Ford Sony system.