Signal lights suddenly stop working

Did you ever change the signal flasher relay? Also, pop your hazard switch out and check that all the wires connected to it make a good connection and are tight. I had this same problem, turned out that the signal wires that run through the the hazard switch had came loose

87-95 Mustang Turn signal troubleshooting

Please note that the wire colors changed periodically; be sure to use the wiring diagram for your year car!

The ignition switch is also known for creating turn signal problems. Make sure the ignition switch and wiring are in good shape as a first item to check. This is especially true if you are having problems with things like the radio and heater/AC blower.

Ignition switch wiring


Some of the symptoms of ignition switch problems are things that don’t work or are intermittent like radio, turn signals, wipers or heater. The auto parts stores sell the switches for $13-$15.







While you are working on the switch, check the wiring and connector closely. A replacement connector with new wiring pigtails is available from most auto parts stores

AutoZone and Advanced Auto Parts have the same Part Number: 434 - may have to order, not always in stock

Advanced Auto Parts alternate part number: PT5534



If just the plastic shell is broken, a small jewelers screwdriver inserted from the front will release the contacts from the connector shell. Do this one wire at time and insert the wire and connector you removed into the same position on the replacement connector shell.

Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly

Torx bit set from Advance Auto Parts



Autocraft torx bit set – have small hole in tip for tamper proof screws.
Part No. AC571/W1386 Cost approx. $12 +tax



87-95 Mustang Turn signal troubleshooting



Keep in mind that the flasher on the front of the fuse panel is for the hazard flasher. Locate the turn signal flasher, depending on the model year it may be behind the radio or on the backside of the fuse panel or behind the glove compartment.

Turn the ignition switch to Run; the engine does not need to be running for these tests. With the turn signal flasher removed, test the pink/orange wire for 12 volts.

Set the voltmeter to DC volts and select the scale that is closest to 12 volts. Clip one voltmeter probe on the bare metal part of the car body for a ground and put the other probe in the turn signal flasher socket contact that has the pink/orange wire. You should see about 12 volts.

No 12 volts present: replace the fuse and check for 12 volts again as described above. Do not turn the ignition switch off if you are testing for voltage.

Still no 12 volts, pull the fuse and test the #5 fuse socket contacts for 12 volts. One contact will have 12 volts. One probe is grounded, the other probe gets stuck in the fuse contacts. Test both contacts for 12 volts.

No 12 volts on either fuse contact, the ignition switch or ignition switch wiring is suspect. Move things around so that you can get to the backside of the ignition switch wiring connector with the ignition switch still connected to it. Make sure that you don't turn the ignition switch OFF while you are testing it. It still needs to be in the Run position. Look for 12 volts on the large gray/yellow wire. No 12 volts and you have a bad ignition switch or some bad wiring. Wiggle the large gray/yellow wire to see if it gets or loses voltage while you are checking it.

Diagrams courtesy of Tmoss & Stang&2birds

Fuse box layout


Ignition switch wiring


Once you have located the turn signal flasher, remove it from its socket and jumper the socket contacts together. Turn the ignition switch to Run and try both left and right turn signals. They should come on steady if you have good 12 volts to the pink/orange wire. If the lights turn on steady and bright, that means the flasher is suspect. If you find one more bulbs do not come on steady and bright, then you have either a bad bulb, bad ground at the bulb socket or a corroded or bad socket.

If you still have problems, then it is the multifunction switch, or its wiring; that is a case of last resort.

Multifunction turn signal switch:
Before you think about replacing the multifunction switch with one from the junkyard, here are some things to be aware of...

The problem is more common in GT models because they had fog lights on the same power wiring as the headlights. Ford undersized the wire and that caused problems.

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.

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

The following diagram is for 87-89 model cars.

Turn signal switch wiring:



The following diagram is for 90-93 model cars.

Turn signal switch wiring:



The following diagram is for ]94-95 cars
Diagram courtesy of Tmoss & Stang&2birds