Can I charge an iPad from a 14 volt cigarette lighter socket?
Yes, but you have to check the input range of the adapter.

DC voltages in a car can vary between 10V (at rest) and 16V (charging).   Most USB chargers you buy can handle this variance.

However, there are some applications where the voltage can be (much) higher like aviation, trucking, and marine where the voltages can reach up to 24 volts.

This is where paying attention to the specifications and buying high quality is very important. Here are two high quality ones that I personally use 


Scosche Dual ReVolt - Up to 16V
Anker PowerDrive Speed 2 Ports - Up to 24V


I use the Scoshe mostly because it's low profile and I can close the ash tray door with it still plugged in (though it always gets "appropriated" by someone else).