Hi I have a 2003 mustang 3.8 v6, the issue I'm having is my blinkers, my break lights including the third brake light, my interior dome light as well as the two lights on the sides of the dome light the door locks and the mirror controls all stopped working at the same time I've checked the fuses under the dash and under the hood I've checked the flasher relay under the dash and the blinker switch on the steering collum I've also checked the rke module or whatever module it is that's in the trunk on the drives side all seems to be in correct working order and yet I still have no blinkers or brake lights the only conclusion I can come to is its a ground wire somewhere I checked the ground wires under the dash on the passenger side right below the radio I believe there's another ground somewheres in that area I could really use some help cause it's been a total brain buster for me I've been searching for what could be the issue for exactly one week now

 

Could it be the headlight switch and/or wiring harness?

I was having a issue with headlights, tail lights, and left rear blinkers. All were intermittently working. Mostly, I had no tail lights or blinkers. Long story short, the wiring harness had a short (it even burned and melted some plastic). I replaced the two, and it cured all the symptoms.

Maybe pop out your gauge cluster and inspect the headlight switch?

However, I'm not sure it would relate to the mirror controls and door locks.