Advance trac
 

My service advance trac and abs lights come on snd off continuously as I drive my 2014 mustang gt. I have to keep my finger on the button to turn it off due to it turning itself back on in the next 5 seconds. Sometimes the button will not turn it off and the car acts like it’s braking itself then it will ding snd all turn off or on. My dealership is horrible. Csn anyone point me in the direction to begin replacing parts . Ironically my billy dog tuner locked up the second I plugged it in to find the codes for this.

Could be 1 of many things from a Speed Sensor to the steering rack and many thing in between. It needs to be diagnosed before you start throwing Benjamins at it.

See this thread for something you can check: Service Advancetrac PROBLEM SOLVED - The Mustang Source - Ford Mustang Forums

but I don't think that is the issue in your case, it sounds like something more complicated, maybe a computer or sensor-related fault ... I think I would be looking for another dealer who seems to know what they are talking about and might help

Find a local shop that is decent, or a new dealership. With a hard fault like that, something is healthily wrong with the car, and should be a pretty easy diagnostic.