7.3L Powerstroke Ignition power source.  Arrow is pointing to red wire with yellow trace.  This round black plug is attached to the metal dash chassis just above.  Use the same ground location used in the previous image (6.0L Powerstroke).
NOTE: There are many different locations where you can obtain your ignition switched 12V source. Depicted above is just one example.  Irregardless of where you connect your gauge power and illumination source, we recommend that you check this sources first, before you make your connections.  For 12V Ign. switched: Using a voltmeter, ground the black lead from the meter to chassis ground. With the red lead off the meter, probe the 12V Ign. switched source.  You should read 12-13VDC when the Ign. key is turned on, and 0V when the key is off.