Particularly useful for a universal fit android headunit with is ISO connectors this is quite straight forward to power up. For the custom fit android headunits some information will be needed to discover which pins need the power to get it to boot.
The GND wire is part of the ISO standard so color is 99.99% of the time black and may be the thicker of the two black wires if there is more than one. Position A8 of the ISO power plug is reserved for GND connection.