Lead-wire splitters come in pairs: one will be for the negative lead and one for the positive lead.
1. Connect the female end of the Red lead-wire to the Red lead coming out of your Contour M2 device.
2. Connect the female end of the Black lead-wire to the Black lead coming out of your Contour M2 device.
You have successfully split a channel.
Note: There is no need to worry about which gel pad has the RED (positive) wire or the Black(negative) wire. Just be sure to have a Red and a Black wire from the same channel placed on the same muscle group.