Troubleshooting Sequential Turn Signals

This article covers troubleshooting 1967-1968 Mercury Cougar sequential turn signals. While most the information has been acquired through experience on a 1968 model, the ideas can be applied when servicing a 1967 model too. This information is also applicable to 1967-early 1969 T-Birds as they share the same basic design.

The turn signal system has five electro-mechanical parts: the turn signal switch, (located in the steering column), a turn signal relay (located under the dash), a directional relay, an emergency relay, and a motor-driven sequencer (located in the driver's side trunk under the mat or behind the backseat in T-Birds). The 1967 system also has an emergency relay and a turn indicator relay under the dash. The most failure prone parts are the mechanical sequencer, the turn signal switch, and the emergency relay in the trunk. Circuit diagrams may be found in the appropriate year factory shop manual.

Basically, the system works as follows: when the directional lever on the turn signal switch is moved, it completes circuits that select and feed power to the corresponding bank of lights. Power for the lights is fed from the fuse to the turn signal switch, then on through the turn signal relay to the sequencer. The sequencer has three cams that, when rotated, depress switches corresponding to the inboard, center, and outboard tail lights. The power is then routed first through the emergency relay (which disconnects all but the center light if the emergency switch is on for Cougars and connects all lights together for T-Birds.) and then to the directional relay. This two-sectioned (right and left) relay routes power through to the selected bank of lights. Since brake lights are not sequenced, the directional relay allows all lights to turn on simultaneously when the brake light power feed is energized. But when the turn signal switch is actuated, the brake light power feed is disconnected and the turn signal feed is activated to allow the directional signal to override the brake lights.

Now that you understand a little about how your turn signal system works, you can start troubleshooting. You will need a VOM (Volt-Ohm-Meter) and the circuit diagram for your year car. The most common complaints are: no turn signals, one or more lights on but not flashing, one or more lights flashing, and center and front lights only flashing. The first place to check is the in-line fuse under the dash to the right the steering column. The next stop is to check all bulbs and their sockets. If these are all good, then now the real sleuthing must begin!

No turn signals (right or left):

When the turn signal lever is depressed, no lights come on anywhere. A click from the directional relay in the trunk may be heard. Start by checking for 12V power on the orange/green wire feeding the motor-driven sequencer in the trunk. Lack of power indicates either a bad turn signal switch or fuse. The 15A turn signal fuse, for the Cougars, is located in a white twist-apart fuse holder tucked up under the dash to the right of the steering column.

Next try depressing the emergency switch, if the emergency flashers work, the turn signal switch is most likely bad. Disconnect the turn signal switch from the harness and check it according to Table 1 using a VOM or self powered test light. The table shows wire pairs that should be shorted together with the switch in the indicated position. If any connections are open, replace the switch. Usually the switch has failed when the plastic around the riveted contacts in the area around the emergency button appears to be burnt or melted. This can only be seen with the steering wheel removed. The turn signal switch connector pins can also be burnt or oxidized: carefully inspect the pins on both sides of the connector. Make sure they are all securely seated into the connector and the connector is not melted or burned. For more information, review the Turn Signal Switch Diagnosis Guide.

Table 1. 1967 or 1968 Turn signal switch connections

No left turn signals:

No right turn signals:

Some or all lights on but not flashing:

This usually means that the motor in the sequencer has quit. Remove the white cover from the sequencer and see if the motor is turning the cam. FORD has discontinued the unit but an electronic replacement is available.

One or more lights flashing:

If all bulbs are OK, the trouble is most likely in the sequencer. The switch contacts erode away with age. Sometimes they can be cleaned up with an ignition points file, but this is just a temporary fix. The best solution is to replace the sequencer with an electronic unit.

Center and front light flashing only:

This is the normal mode for the emergency lights on a Cougar, but will occur if the emergency relay fails. If a replacement electronic system has been installed, make sure that the single wire with the 1/4" quick disconnect male is plugged into the emergency relay light blue wire socket in the trunk.
Note: This wire is only present on electronic systems built before 1/1/22. Later systems automatically detect the emergency flasher mode and do not use this wire connection.

Dash indicator light doesn't flash:

Often the dash indicator lights will only flash once or just change from bright, to dim, then dimmer as the rear tail light sequence progresses. The indicator relay is calibrated to click and operate the dash light when all four 1157 bulbs (1 in front, and 3 in back) are working - check the bulbs first. A low battery, weak charging system, bad connections in the turn signal switch, or weak K5/K7 indicator relay can cause this problem. When LED bulbs are used, the indicator lights will not flash because the relay is calibrated for the much heavier currrent draw of 1157 bulbs. A electronic replacement relay is available.

Table 2a. OEM Service Parts list

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Table 3. Replacement Parts list

08/24/24 SEQTS

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