My 69 Mustang tail lights flash on and off when the ign switch is on. Brake and turn signal lights work as they should but as soon as I turn off turn signals or release brake pedal tail lights start flashing again. Grounds check out ok and bulbs are 1157s. Sockets look good. So I had to unplug the turn signal blinker to stop lights from blinking. It's not the 4 way blinker that's making the blinker noise. What am I missing here ?