Blinkers, taillights, brakelights messin up

When you have the headlights on, and you turn on either left or right blinker, they both start flashing and when you apply the brakes, the blinker lights come on solid as breaklights. Does anybody know what could be causing this problem?

Check the electrical connectors at the rear brake lights, at the bulbholder units. They tend to corrode & lose ground connections.