External Speakers 2005 Safari

[PovIndy]

We want to hookup external speakers for our 2005 Safari. We do have a speaker selector switch which lists " IN - Out - Both" positions
the IN position plays the front compartment speakers and the bedroom speakers - the Out position plays only the front compartment speakers - the both position plays only the front compartment speakers. I have followed this forum where it addresses the exterior - flat 4 speaker outlet found on some of the trailers in this time frame - but our 2005 Safari does not have this outlet. I would like to add that outlet to our trailer. I am sure I can find an exterior weather protected flat 4 outlet to mount on the rocker panel. My questions are - what is the best way to tap into the speaker selector switch? Does anyone have a schematic of how that switch is wired to distribute the output from the Head unit to the various speaker pairs? Is that the best way to wire another set of speakers? Then once I have tapped into the speaker selector switch what is the best way to fish the wires through the wall and out the floor to the rocker panel area beside the door?