No wiring diagrams or schematics published for CX models to my knowledge and I suspect there never will be. You will need to go back to basics.
Probably best making such a socket permanently live with suitable fuse say 15 amp. You could tap off the feed to existing USB socket since that will be 12 volts but you may need to increase fuse rating. Not familiar with CX series but the fuse box should be labelled. Another possibility is to re-purpose an unused circuit for an option not taken up, heated seats for example, as the wiring will already be in loom.
