Usually you select the speaker system on the Radio/DVD player. Check the manual for it. As for a wiring diagram, good luck there is little documentation on most of the models. Some owners of the high dollar units have been able to obtain some information and some owners have managed to compile information from their unit. If after locating the switch/button for the external speakers, they still don't work, pull out the DVD/Radio as some members have found not all wiring is connected of connected properly. If you pull out the unit, I suggest you have materials ready to cut and reconnect the wiring as the factory method is a problem waiting to happen. Just a word of caution. Always turn off the outside speakers after using them You don't want them on some rainy night when you decide to sit inside and watch a movie.
2015 Freedom Express 248RBS
TV 2015 Silverado HD2500 Duramax
TST Tire Monitors
Honda 2000I + Companion
2 100W solar panels