DO NOT peirce the wires like they did in that pic
you need to backprobe the wires. put the pins into the back of the connecter where the wires go into it.
piercing the wires like that will cause moisture to get into the wires and corrode them
it's easy to find which wire is the signal. put one multimeter lead on negative then the other lead on each wire. one should read battery voltage (power, 12v), one should read 0-0.2v (ground), and one should read around .9 (signal)