Be sure to match the wire color with the B-R-W color-coding on the boards. The white wires will be adjacent to each other in the center of the connectors when properly attached.
Although it's not required, labelling your cables with a small piece of masking tape (close to the unconnected ends of the cables) will make it significantly easier to make the DHB-10 connections later on in the assembly guide. Be sure to orient your encoders correctly when labelling. Left (LA, LB) and right (RA, RB) labels should correspond to your left and right sides.