As I recall with our 2007 E350 chassis, the 12V outlet higher up, the one with the square boot/cover, is a low wattage outlet. Using the cigarette lighter or other high power device in that upper outlet will blow it's fuse. The lower outlet handles much more power as observed by much much (much) heavier gauge wires to it. I tapped into the lower outlet to power the extra 12V outlets I installed in the cup holder area.
frecklestweety, If you are at your wits-end trying to find the blown fuse for the dash board square-covered 12V outlet, one by one, remove, inspect, and re-insert each fuse until you find the one that is broken inside. I suspect it has a lower number like 10 or less. Do the same in back for your PC-installed 12V outlet above the passenger seat. I wonder if your GPS is a power hog which is blowing the low amp fuses. I would dedicate it's use to the lower cigarette lighter which offers much more power, even though it is in your way of shifting gears. It is for that very reason why I added the two extra outlets into the front of the cup holder unit. I wanted the wires away from the gear shift lever and off the surface of the cup holder.
Here are the outlets in discussion seen on our rig. You can also see the two extra outlets I added in the cup holder.
