If you have the S10-specific one, I'm assuming you have a 2-switched/1-unswitched or all-3-switched version. The purpose of the S10-specific unit from EB is to have a plug and play solution for turning the switched circuits on. That is what the connector for the bike's auxiliary light connector does.
You can see on EB's site that he has a version of the 3CS that taps into a switched wire—like the taillight wire—to turn things on:
http://easternbeaver.com/Main/Wiring_Kits/Fuseboxes/3_Circuit/3_circuit.html
What I can't tell from photos of the S10 3CS is whether it's 2 wires on that connector or 1 (I'm pretty sure it's 2 given how it compares to the standard 3CS). If it's 2, you would need to re-route the black wire from that connector to a ground somewhere. You may be able to simply tie that in to the battery grounds (black wires) that're already coming off the connectors or you could crimp on a ring terminal and add it to the battery post.
The blue wire would then just need to be stripped and you could use a PosiTap to draw power from the taillight or other switched circuit.
