Are you referring to the Y-harness HD includes in the Air Wing luggage rack LED? Here are the installation instructions, but HD says it's not available for separate sale and doesn't provide a p/n, at least in these instructions:
http://www.harley-davidson.com/en_US/Media/downloads/Service/isheets/-J04669.pdfI'm 95% sure I saw a p/n for this harness, but can't recall how I came across it.
In any case, I have one that a tech at my local dealership gave me and it worked perfectly for wiring the Ultra run/brake lights with the tour pak spoiler LED (after I changed the connector).
You're welcome to it since I have since installed the HD tour pak run/brake/turn signal conversion kit which uses the rear lighting harness and associated connectors/harness, and the spoiler LED is simply wired to the tour pak harness.
Send me a pm with your mailing address and I'll send it to you.
Carl