Hi Jim,
I assume you have a meter that you can test continuity? (measure for a very small resistance).
Typically such a switch has one "pole" on one side and the other pole 180º from the first. One of the channels will be on one pole, the other channel on the other. Here is how you figure out which goes to which. (sometimes you can actually see the mechanism of the switch to see how it works).
[this whole discussion is for one pole = one channel, usually the other channel will be on the other side]
With the switch in an initial position do a bunch of pair wise continuity measurements. There should only be two pairs that have continuity between them. Writing them down sometimes helps to see what is going on. Then move the switch position one spot over and remeasure one of the original pairs, it should not have continuity between, but move one of your meter probes over one spot. If those are continous, then try moving the other probe. The tab that stayed the same is your out for that channel. The other tab for which this is continuous with will move one position over each time you move the switch position. These are your successive "ins". Hook up each hot wire from each source to these ins, and one wire from the out to the center of the out RCA. Do the same proceedure for the other channel, but you should see the pattern already.
