I'm referring to the OEM 18pin amplifier output connector. There is also the 12pin input, if that has any significance. It's possible I may even use that if the 375watt per channel on the new amp is too much and I can't reduce it properly. The HU as a digital preamp of 50watts per channel, supposedly. I already have the front speakers tapped into the 18pin oem output connector through the new amp which is connected to the headunit via a single pair of RCAs. The HU has only one pair of left right outputs, although it recognizes left, right, front, and rear fading and stereo is in fact stereo. There is also a single RCA for mono sub, two single RCA video inputs, one triggered by the reverse lights, one for dashcam, and one video output I'm guessing for an alternative external recording device, because it has also a USB port on the back, I assume, for expanded storage. Oh and a mic input. I have yet to get to all these features as every spare moment I have for this has gone to the music. And the instruction manual was pitiful. 4 pages of microscopic text in poorly translated English. It's also missing, but was useless for my needs anyway.