The lead from the esc plugs into the Castle link, unplug it from the rcvr and plug it into the Link. Get the PC setup and running the software then make the connection. You'll see the two boxes on the front that were red, turn green as the link sees power from the USB and then the esc.

You may need to upgrade the Link software version to have the later options which include the variable LVC under auto lipo. Depends on where you dnloaded the Link software from - the included mini-CD was outdated with mine. Dnloading from Castle's site will give you the latest version of teh Link software.

I use it, mine is set at 3.4v/c so I know its there.