if it is in the mustang in your avatar i had the same problem.
turned out to be a wire slipping out of the wire harness behind the fog light switch on the lower dash piece near the shifter.must have happened while i was swapping radio parts.
are you testing with the headlamps on?think the power comes from the multifunction switch
what year and model mustang is it sal ?
are you testing with the headlamps on?think the power comes from the multifunction switch