These days many may find multiple different wires schemes running from factory head unit, and depending on the aftermarket system, want to find the right pair to get the job done.
When adding an aftermarket sub system, some head units provide a dedicated sub channel output. If that option is not available, tap into the channel output that provides a sub frequencies signal; whether it be front or rear channels. From there you would run from the ‘Bass Output’ to the bass amp. The ‘Bass Output’ has a low-pass filter starting at 1kHz, and the PFM roll’s-off the low end at 33Hz.
The LC2i can also handle an aftermarket speaker system. The main output is designed to send signal to an amp for a car speaker system. Make sure the signal going to the input of the LC2i is a full range signal otherwise it will not sound right. Ensure that the aftermarket amp has a 2 channel option for its 4 speaker outputs. Keep in mind, the LC2i is only a two channel input and will accept only one pair of Left/Right signal, leaving a loss of Fade control… So choose Wisely, for the true signal will bring you life, the false signal will take it from you!
Lastly, Some aftermarket sub amps only require a mono signal. In that case, use the ‘Left Speaker Input’ on the LC2i and out the ‘Left Bass Output’ to the amp. Note: The GTO signal sense only activate when receiving signal from the ‘Left Speaker Input.’