Just a quick addition to the debate. I have a later cmax but have 2 12v sockets in the cabin as well as one in the boot. Both cabin sockets are fed by the same fuse, not sure about the boot. Having checked with a meter, my problem was that the socket adjacent to the cup holders didn't work but the other (centre console facing the centre rear seat) did.
My assumption is that the previous owner spilled something into the socket as I used a dremel with wire brush attachment (having first removed the fuse) to carefully clean the socket to restore functionality.
Possibly worth a clean before going to the hassle of running new cabling?
Black 59 Plate 1.6L TDCi Titanium/Privacy/Parking/USB