If you have a Freightliner Chassis, look in the front drivers side compartment where all the fuses/relays are located.
There should be a fuseblock chart on the bottom of the compartment, look at this chart at the ignition or Fuseblock "A". You want to find the listing for the fuse "TV Relay - Ign. Defeat". On mine it is fuse position B3 listed as a 5A fuse but mine had a 10A fuse in it.
Remove the cover for the Fuseblock "A" or ignition feed fuseblock. You want to remove the fuse described above or according to your fuse chart.
This should disable the relay over ride that shuts off the 110v power to the TV when the ignition switch is turned on and while driving, at least it does on mine.
Let me know how it does, Oh just one thing, it is illegal in most states for the TV to be on that the driver can view while in the drivers seat.