Aftermarket HU Power trouble

Hey so I've got a 2002 w210 and a new Boss HU. All wires are connected properly from the constant 12v battery wire to the 12V accessory wire through the adapter but still no power. I looked at a diagram of the wire functions of the oem harness and the adapter matches up with the memory power wire but not the 12v acc wire, the one that actually matters. I saw a youtube video suggesting to look for power through the cigarette lighter but I'd be happy to take any suggestions before I get into that