Here is the original post which talk about how to create a 0-10v control cable for use with a Kessil A360 and the ALC 2 pin 0-10v controller. This probably tells you which is + and - to those who understand such basic things better than I.
"Then the right and white has the hots for the reds on the ALC..." So it would appear on that above picture of the ALC on top of the yellow felt, it is the one with the red wires that is +, i.e., the one on the left.
See here:
http://www.reefcentral.com/forums/sh...ght=kessil+alc