Don't do that unless you KNOW which wires are the remote (12V), constant (12V), and ground coming from the HU. Then all you have to do is put the 2 12Vs together on the + and ground to chassis. But, it's not safe if you're not sure. Not only will you fry it, but you'll burn it up, or even worse get that 800 or so amps flowing through you.
