Was trying to wire up the new/used head unit today. Got all the power plugs wired up, but couldn't get it to power up. I checked the obvious, Red to Red, Yellow to Yellow, etc. I plugged in the old head unit. No power. Then I found by plugging this wire pictured below it had power again. My question to you audio guys is, what the hell is this wire used for? I know it is what is holding me back, I just dont know where to wire it to. I have the wire pictured below and if I need to ill snap a picture of the head units wires. Thanks in advanced.
(Yes, I know it's a weird floormat...)