The one thats going to the right?
Its the RCA cable that carries the signal out of the LOC and sends it to the amp.
I'd also like to point out, for better understanding, that the wires the red and yellow arrows are point to were once connected. The signal from the factory amp, instead of being send directly to the speakers, is now sent to the LOC, which converts the signal for the RCAs to carry to the amp. The amp processes the sound and sends it back to the yellow arrows wires which lead to the speakers.