I came across this stereo "switching" jack on ebay yesterday.
http://cgi.ebay.com/Fishman-Switchcr...item27b6908773
This is the kind of stereo jack that you need to handle dual sources when one or both of the sources is an active system. With this kind of jack, the longest contact tab is connected to the battery's negative lead. The shortest contact tab is the tip contact and the second shortest tab is the ring contact. The sleeve is ground.
Here's the diagram for the "switchjack" off the Fishman website:
http://www.fishman.com/files/switchjack_user_guide.pdf
Gary