I had same issue, was told there will be a power source in the back, which now there is not. BUT….they done this just to save money as the wiring is there in the boot for a usb port or 12v post. When you open the boot, on the left hand side there is a round plastic hole, pop it off and there are 2 wires there, which are not connected to anything, so if you get a usb/12v port on amazon or any where really, just need to connect the wires and push the new device in. Pics attached to see. Ive not done it myself yet,but I will be.
It won’t let me attach pictures for some reason, but I hope it helps