Electrical Panel Dimmer

check your TFI stalk switch. The flasher relay is either inder the dash or open the glove box and it is inside to the left.

it is the lever on the left side of the column that you use for the directionals and the wipers. Sorry dont know why I put TFI. It is the Multi Function Swtich. You have two flasher relays the one on the fuse box is for the flashers and the one behind the glove box by the radio is for the turn signals. Check those first.

The wires for the MFI switch are known to go bad. Here is a good post on your problem

http://www.stangnet.com/mustang-forums/threads/turn-signal-problems.785566/

It’s time for an Easter egg hunt…

The turn signal flasher is not mounted on the front of the fuse panel. The flasher on the front of the fuse panel is a separate one for the hazard lights. The turn signal flasher is in one of several places, depending on when your car was made. Some are behind the fuse panel on the back side, others are behind the radio and some are behind the glove box.

Other possible problem sources for the turn signal malfunction are the ignition switch, multifunction switch and the plastic shell that holds the turn signal wiring connector pins.

A word of caution about multifunction switches is in order here. The multifunction switch (high/low beam, wiper, turn signals) are different for different years. 87-89 will work in any 87-89 car. The 90-93 switches only work in 90-93 cars. You can't put an early model switch in a late model car, nor can you put a late model switch in an early car.

Supposedly you can move the pins around to make the switches work in model years that are different from the car the switch came out of. I cannot verify that and haven’t tried it .

The following diagram is for 87-89 model cars.

Turn signal switch wiring: