what could cause both blinkers not to work but both come on when the brake is applied? it just started today so i have no clue yet. oh its a 1970 mustang by the way.

 

The signal lights do not have a proper ground connection,and when the brake lights are activated the circuit is running through the filament in the tail light bulb and using it as a ground. Make sure all ground wires are connected and have clean metal to metal connections. BTW, I'm not sure about the coupes but if you have turn signal lights in the front that bolt to under side of the front bumper like the Mach 1's do then you need to have the front lights connected to the bumper. (If the bumpers are on the car). The turn signal lights use there housing as a ground circuit and it completes to ground by the bolt connection to the bumper.

 

Check the flasher its under the dash maybe on the fuse box it looks like this
http://www1.autozone.com/