Urbestfriend recommended searching for the manual. I just got
an updated e-mail from one of my previous sources for down-loading.
http://www.digital-manual.com (was holdbarbike.com)
For the Xciting, the wiring schematic is on page 420 of 420.
Unfortunately, I can't get the page for you.
I can tell you that once you gain access to the rear wiring.
(Remove Battery, Battery Box, maybe rear rack and top
cover, you can pretty much follow your wires down to
the particular light. If I recall all Grounds are Brown.
I still recommend paying a few bucks to get the whole
420 Page download.