OBD2 port construction, Toyota Camry 95, and Dodge Durango 2002

The port runs at battery/system power, which is usually anywhere from ~12-15vdc, depending on the specific system (manufacturer) and how fast the engine is running (voltage a little bit higher when revving higher). If the device is designed to plug into the OBDII port for power, then it is designed to handle these variances, because the power going to the port is going to vary.

To power the device, there should be two pins you are worried about: ground/earth (-) and the power (+). You can find them here in the port:

The pins you are looking at are 4 & 16. Your device should be the opposite of this, but hopefully you can figure out which is which. All you need to do is apply the power to pin 16 and provide a ground/earth at 4 and your device is powered. You can pull power from the fuse panel or design something from the cigarette lighter (or power) socket. If you are looking to use a Data Link Connector (DLC) to connect your device to (so it would be just like under the dash), you can find one easily at a junk yard for cheap ... just ensure you've got a long enough pig tail attached to provide for your wired connection. Almost all cars (at least here in the States) which are 96 and newer will have one.