Running a tail lights stay on - 2010 Ford F-350 Super Duty

Your park/ headlights should have power when the key is in the off position. I would look at your headlight switch.

Tail lights or brake lights? If its the running lights it might be switch if its brake lights then its what guy b4 me said.

Is it the brake light or the running lights, are all the lights on went the ignition is in the off position and the light switch is in the off positions aswell or the brake lights are on including the third brake light?

its your running light fuse under driver dash board or on side of it

more than likely its a stuck brake light switch

either a stop or turn signal or tail lights are out

Remove the tail light, then the grey bar with all the lights by removing the two screws at the top and bottom. play with the light socket that dosen't work and chances are that it is cracked and broken. If it is broken then the contacts within are not making contacts becuase the black plastic socket is used to hold the contacts together. If you are handy, you can tear open the grey bar and solder the contacts together, then epoxy the bar back together. Or, find, purchase and replace the grey light socket bar.

Check for a sticking running light relay.

Are you sure they aren't the stoplights (brake lights)? There should be a stoplight switch connected to the brake pedal and replacing it would correct the problem. If it is the tail and parking lights, you must need a new switch that controls them. Signed, 64 year old car guy.