Article 1268 - Turn Signal Indicator Light Operation and Problem Diagnosis

TSB #84 Supplement - January 26, 1978
(All 1968 Thunderbirds)


Reports have been received from the field indicating that complaints of malfunctioning instrument panel turn signal indicator lights are being encountered on some 1968 Thunderbirds. This article contains explanations of system operation, updated wiring diagrams, and diagnosis guides to assist you in correcting complaint units. In order to insure customer satisfaction it will be necessary for you to follow the step by step procedure as outlined in Part I for vehicles built prior to mid-November with the sequential dash indicator light feature, and Part II for vehicles built after mid-November without the sequential dash indicator light feature.

The wiring diagrams contained in this article update and supersede the one appearing in the 1968 Wiring and Vacuum Diagrams Book (page 6-E7).

PART I - 1968 Thunderbirds Built Prior to Mid-November 1967 With Sequential Dash Indicator Light Feature

SYSTEM OPERATION:
The 1968 turn signal and emergency flasher system on units built before November is basically similar to 1967 except for some revisions to provide for sequentially operating turn indicator lights in the instrument panel. The major differences include deletion of one rear mounted relay (two on units equipped with overhead convenience panel), revision of the turn signal indicator relay (from normally closed to normally open), redesign of the instrument panel indicator lamp system, and wiring changes to accommodate these changes.

The sequencing effect is produced by two bulbs, one behind each of the outer lenses in the dash mounted indicator light panel. When the turn signal switch is actuated, the bulb opposite the side of the turn selected illuminates and is followed immediately by a flash of the bulb on the side of the turn selected. This flashing of the two bulbs behind the three lenses gives the appearance of a "pointing beam of light" toward the direction of the turn selected.

The following is a brief explanation of the electrical operation of this system. When the turn signal switch is actuated for a right hand turn and the rear lamps begin to sequence, the left dash indicator bulb is illuminated by electrical feed from the same circuit which feeds the right front exterior turn signal lamp. As the rear lamps sequence to the point where all three bulbs are illuminated, the contacts close in the turn indicator relay (mounted under right side of instrument panel) providing electrical feed to the right dash indicator bulb and to the ground side of the left dash indicator bulb. This condition causes the left dash indicator bulb to go out (electricity flowing to the bulb from both directions acts as a switch to turn off the bulb) and the right dash indicator bulb to illuminate. The ground for the right dash indicator bulb is provided through the unused feed circuit to the left front exterior turn signal lamp. This operation is repeated each time the rear lamps complete a full sequence.

PROBLEM DIAGNOSIS:
Before attempting to diagnose a problem with the instrument panel indicator lights, make sure that the external turn signal lights are operating properly (refer to the 1967 Ford Thunderbird Shop Manual for external turn signal light problem diagnosis and the wiring diagram included with this article). Also check to see that the battery specific gravity reads above 1.225 (this affects operation of the turn signal indicator relay).

Follow the diagnosis procedure that applies to the customer complaint as indicated by the bold type and repair as necessary.

BULB DOES NOT LIGHT ON THE OPPOSITE SIDE OF THE TURN SELECTED (No Sequential Effect)
• Defective bulb — remove bulb and check continuity through the filament.
IF O.K. CHECK FOR
• Bulb or bulb socket not making proper contact in the printed circuit — inspect for improper installation, foreign material, etc.
IF O.K. CHECK FOR
• Open circuit between the printed circuit (instrument panel) connector and the < splice of the indicator bulb circuit to the front turn signal lamp feed wire — disconnect the multiple connector at the instrument cluster printed circuit. With the turn signals running, use a 12 volt test light to check for intermittent feed at the white/blue wire for right bulb and/or at the green/white wire for the left bulb.
IF O.K. CHECK FOR
• Open circuit in the printed circuit for feed or ground — check the printed circuit in the instrument cluster for continuity in the affected circuits between the connector terminations and the individual bulbs. Make sure that the multiple connector is making good contact to the printed circuit.

BOTH BULBS FLASH DIMLY AND TOGETHER IN EITHER TURN POSITION (No Sequential Effect)
• Defective turn signal indicator relay (under right side of instrument panel) — With the turn signals running use a 12
volt test light to check for intermittent feed at the brown wire coming from the relay.
IF O.K. CHECK FOR
• Open circuit between the indicator relay and the connector at the steering column wiring — with the turn signals running use a 12 volt test light to check for intermittent feed at the brown wire in the three wire connector labeled "D" in the wiring diagram; check for feed on both sides of the connector to make sure electricity is flowing through connector.
IF O.K. CHECK FOR
• Defective turn signal switch and/or wiring assembly in the steering column — with the turn signals running, use a 12 volt test light to check for intermittent feed at the yellow wire in the three wire connector labeled "D" in the wiring diagram; check for feed on both sides of the connector to make sure electricity is flowing through connector.
IF O.K. CHECK FOR
• Open circuit between steering column wiring and instrument cluster printed circuit — disconnect the multiple connector at the instrument cluster printed circuit. With the turn signals running check for intermittent feed at the violet wire in the multiple connector.
IF O.K. CHECK FOR
• Open circuit in the instrument cluster printed circuit — check the printed circuit for continuity in the circuit #17 (see 1968 Wiring Diagrams Book, Page 6-E3). Also make sure that the connector has good contact to the printed circuit.

INDIVIDUAL BULBS FLASH DIMLY DURING SEQUENTIAL OPERATION ON THE SIDE OF THE TURN SELECTED
• Poor contact of the bulb or bulb socket to the common ground (circuit #17) in the instrument cluster printed circuit
— inspect for improper installation, foreign material, etc.
IF O.K. CHECK FOR
• One of the two resistance ground circuits is disconnected or broken — check grounds labeled "B" on wiring diagram located on left and right cowl for proper connection to sheet metal using star washers. Also use an ohmmeter to check for continuity between violet wire at printed circuit multiple connector and a good ground, should read approximately 5 ohms.

BOTH BULBS OPERATE BUT EACH FLASHES ONLY ON THE OPPOSITE SIDE OF TURN SELECTED (right turn — only left indicator flashes and vice versa) BATTERY AND EXTERIOR LIGHTS OK
• Defective turn signal indicator relay (under right side of instrument panel) — with the turn signals running, use a 12 volt test light to check for intermittent feed at the brown wire coming from the relay.
IF O.K. CHECK FOR
• Open circuit between the indicator relay and the connector at the steering column wiring — with the turn signals running use a 12 volt test light to check for intermittent feed at the brown wire in the three wire connector labeled "D" in the wiring diagram, check for feed on both sides of the connector to make sure electricity is flowing through connector.
IF O.K. CHECK FOR
• Defective turn signal switch and/or wiring assembly in the steering column — with the turn signals running, use a 12 volt test light to check for intermittent feed at the yellow wire in the three wire connector labeled "D" in the wiring diagram, check for feed on both sides of the connector to make sure electricity is flowing through connector.
IF O.K. CHECK FOR
• Open circuit between the turn signal switch wiring connector and the splice in the main body wiring harness(14A005)
— separate the four terminal red connectors under the left side of the instrument panel (labeled "M" on wiring diagram) and use a 12 volt test light to check for intermittent feed at the violet wire leading to the female terminal of the connector, if no feed open circuit exists. The wire splice (labeled "N" in the wiring diagram) is located in the 14A005 harness just above the steering column and is approximately 4 inches to the left of where the wiring lead to the stoplight switch comes out of the harness. Also, as a further indicator that this condition exists, the optional flasher light (overhead convenience panel) will flash during turn signal operation.

BOTH BULBS ARE OPERABLE BUT EACH GLOWS STEADILY ON THE SAME SIDE OF THE TURN SELECTED(right turn — only right indicator light comes oh and it glows steadily and vice versa)
• Defective turn signal indicator relay (under instrument panel) — with the turn signals running use a 12 volt test light to check for constant feed at the brown wire coming from the relay. If constant feed exists the relay is defective and should be replaced.
IF FEED IS INTERMITTENT CHECK FOR
• Short or improperly connected wiring to the indicator bulb feed circuit — disconnect turn signal indicator relay, with turn signal switch actuated check for constant feed at violet wire to instrument panel printed circuit connector. If constant feed exists wiring is shorted to a "hot" wire, check for short and repair as required.

NO SET PATTERN OF SEQUENCE — INDICATORS FLASH ERRATICALLY BETWEEN THE TWO BULBS
• Defective turn signal indicator relay (under instrument panel) — check the timing of the feed from the relay (brown wire) using a 12 volt test light. Feed should occur only when all three rear lamps are illuminated and should start as the outboard lamp starts to illuminate.
IF O.K. CHECK FOR
• Inadequate electrical connection in the indicator bulb system
(a) Check the bulbs for positive connection to the printed circuit.
(b) Check the connections of the multiple connector to the printed circuit.
(c) Check the printed circuit for breaks in the circuits that may cause intermittent feed.
(d) Check for intermittent continuity of the circuits involved with the turn indicator bulbs while moving the wiring.
(e) Check all connectors of involved circuits for positive connection and/or foreign matter in the connection that could cause intermittent feed.
(f) Check for secure ground connection in circuits #77 and 77A (Violet Wire).



PART II - 1968 Thunderbirds Built After Mid-November 1967 WITHOUT Sequential Dash Indicator Light Feature

SYSTEM OPERATION:
The turn signal and emergency warning flasher system on vehicles built after mid-November has been revised so that the instrument panel indicator lights will function in a normal manner (left lens flashes when indicating left turn and vice versa with no sequencing action).

To accomplish this change the following revisions were made to the early 1968 system.
• Revised turn signal indicator relay (Part No. C8SZ-13A 366D).
• Revised the wiring of the sequential turn signal relay(Part No. C8SZ-13A366-E).
• Relocated wire terminals in the sequential turn signal flasher (Part No. C8SZ-13350-A).
NOTE: Earlier parts can be reworked to this level by relocating the internal spade connectors in the flasher assembly as shown in the wiring diagram.
• The two jumper wire assemblies at the sequential turn signal relay and flasher are no longer used.
• An overlay (jumper) harness was added under the instrument panel (Part No. C8SZ-13A357A).
• A jumper wire (Part No. C8SZ-15B-583A) and a relay (Part No. C7WY-10B-926B) were added for optional overhead safety convenience panel.
• Two in-line diodes (Part No. C7SZ-10C912-A) are added for vehicles equipped with the optional front fender cornering lights.
• Several circuits in the existing wiring are no longer used.
• Different instrument panel indicator bulbs that are amber in color (Part No. C8SZ-13466-A).
• The center lens of the instrument panel indicator lens panel has been blocked out.

The exterior lamps of this revised system operate in the same manner as earlier sequential systems. However, the front lamps now light at the same time as the outboard rear, rather than inboard lamps during the sequential operation.
The operation of the instrument panel indicator lights has been changed with this revised system and is as follows:

When the turn signal switch is actuated, the feed circuit is energized to the right or left coil of the turn signal relay (in trunk). This same circuit provides feed for the instrument panel indicator bulb on the side of the turn selected. The indicator bulb then seeks ground through a set of normally closed contacts in the turn signal indicator relay. This relay "reads" the number of bulbs illuminated during turn signal operation. When all four exterior bulbs (three rear, one front) of the system are on, the contacts in the turn signal indicator relay are opened, breaking the ground for the indicator light resulting in the flash effect. Therefore, the indicator lights will flash each time the rear lamps go through a sequence cycle.

When the vehicle is equipped with the optional cornering lamps, a diode is provided in the feed circuit for each indicator bulb to prevent a secondary ground condition through the circuit for the opposite side indicator bulb and cornering lamp.

PROBLEM DIAGNOSIS:
Before attempting to diagnose a problem with the instrument panel indicator lights, make sure that the external turn signal lights are operating properly (refer to the 1967 Ford Thunderbird Shop Manual for external turn signal light problem diagnosis and the appropriate wiring diagram in this article). Also check to see that the battery specific gravity reads above 1.225 (this affects operation of the turn signal indicator relay).

Follow the diagnosis procedure that applies to the customer complaint as indicated by the bold type and repair as necessary.

ONE BULB DOES NOT LIGHT
• Defective bulb - check for continuity through bulb filament.
IF O.K. CHECK FOR
• Bulb or bulb socket not making proper contact with the printed circuit - inspect for improper installation, foreign material, etc.
IF O.K. CHECK FOR
• Open circuit in the bulb feed circuit -with turn signals running, use a 12 volt test light to determine if there is electrical feed at the printed circuit at the bulbs.

BOTH BULBS WILL NOT LIGHT
• Defective bulbs - check for continuity through bulb filaments.
IF O.K. CHECK FOR
• Bulbs or bulb sockets not making proper contact with the printed circuit - inspect for proper installation, foreign
material, etc.
IF O.K. CHECK FOR
• Open circuit in the bulb feed circuit - with the turn signals running, use a 12 volt test light to determine if there is electrical feed at the printed circuit at the bulbs.
IF O.K. CHECK FOR
• Open ground circuit between the printed circuit and the turn signal indicator relay - with the turn signals running use a 12 volt test light to check for feed at the brown wire at the turn signal indicator relay, feed should exist.
IF O.K. CHECK FOR
• Inadequate ground connection for the turn signal indicator relay (behind glove box) - check to see that relay is properly grounded to firewall.
IF O.K. CHECK FOR
• Defective turn signal indicator relay (behind glove box) - use a self powered test light to check continuity between center spade terminal and relay case; light should come on.

BOTH BULBS STAY LIGHTED (Do Not Flash)
• Defective outside turn signal bulb(s) - recheck to see that outside bulbs are functioning properly, three sequencing in the rear and one flashing in the front on each side.
IF O.K. CHECK FOR
• Contacts not breaking in turn signal indicator relay (behind glove box) - disconnect three lead connector from the relay and run jumper wires from the outboard spade terminals of the connector to the outboard spade terminals of the relay. With the turn signals running, place a self powered test light across the center spade terminal of the relay and the relay case, the test light should flash off and on.
IF O.K. CHECK FOR
• Short to ground in common ground wire from the indicator bulbs to the relay with the turn signals running, disconnect the multiple connectors affecting the 694 and 77 circuits (see wiring diagram) watching to see when the bulbs go out to determine where short lies.

CORRECT BULB FLASHES, BUT BOTH BULBS GLOW DIMLY BETWEEN FLASHES
• Faulty diodes (with optional cornering lights only) - check diodes for continuity using an ohmmeter, continuity should exist in one direction only.



THUNDERBIRD - EXTERIOR LAMPS & TURN SIGNAL CIRCUITS
EARLY PRODUCTION WITH SEQUENTIAL INDICATOR LAMPS
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1968 THUNDERBIRD - EXTERIOR LAMPS AND TURN SIGNAL CIRCUITS
VEHICLES BUILT AFTER MID-NOVEMBER 1967 - PART 1
1968 THUNDERBIRD - EXTERIOR LAMPS AND TURN SIGNAL CIRCUITS
VEHICLES BUILT AFTER MID-NOVEMBER 1967 - PART 2
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ALSO SEE:
  • Article 1459 - [SUMMARY] - Turn Signal Problem Diagnosis - (1968 Thunderbird) - (from TSB #97 - 8/30/69)

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