Power and Grounds

Battery voltage from the TRN/BCK/UP fuse 22 (C4/C5) or Circuit Breaker 1 (C6/C7/C8) is supplied to the turn signal multifunction switch with the ignition in the run/start position for turn signal operation. Battery voltage from the HAZARD Fuse 7 (C4/C5) or the Circuit Breaker 7 (C6/C7/C8) is supplied at all times to the turn signal multifunction switch for hazard flasher operation. Ground for both front and rear turn signal assemblies is provided at G203. Ground for the turn signal hazard flasher module is provided at G101.

Turn Signals

When the left or right turn signals are activated, ignition voltage is applied through the turn signal switch, the turn signal hazard flasher module, then back to the turn signal multifunction switch. This voltage is then applied through the selected turn signal switch contacts and the front turn signal lamp supply voltage circuit to the front turn signal and the instrument panel cluster (IPC) illuminating the turn signal lamp and indicator. At the same time, this voltage is applied through the selected turn signal switch contacts, the rear stop/turn lamp supply voltage circuit, the appropriate left or right REAR TRN/STOP Fuse (C4/C5) or the Circuit Breaker (C6/C7/C8), and the rear turn signal lamp supply voltage circuit illuminating the rear turn signal lamp.

Trailer Turn Signals (C4 and C5)

Battery voltage from the TRLR fuse, located in the I/P - 1 fuse block, is supplied at all times to the switch side of the LT and RT TRN TRLR Relays located in the I/P - 2 fuse block. Ground for both relays is provided at G103. When the turn signals are active, ignition voltage from the selected rear turn signal supply voltage circuit is also applied to the coil side of the appropriate trailer turn signal relay energizing the relay. With the relay energized, B+ from the TRLR Circuit Breaker is applied through the switch side of the relay and the trailer stop turn lamp supply voltage circuit to the tractor trailer receptacle.

Trailer Turn Signals (C6, C7, and C8)

Battery voltage from the TRLR Circuit Breaker 13, located in the I/P - 1 fuse block, is supplied at all times to the switch side of the LT and RT TRN TRLR Relays located in the I/P - 2 fuse block. Ground for both relays is provided at G103. When the turn signals are active, ignition voltage from the selected front turn signal supply voltage circuit is also applied to the coil side of the appropriate trailer turn signal relay energizing the relay. With the relay energized, B+ from the TRLR Circuit Breaker is applied through the switch side of the relay and the trailer stop turn lamp supply voltage circuit to the tractor trailer receptacle.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Command the left and right turn signals ON and OFF using the turn signal multifunction switch. The turn signals and turn signal indicators should cycle ON and OFF while in the active state, then turn OFF when in the inactive state.

⇒	If all of the turn signals are always OFF, refer to All Turn Signals Inoperative.

⇒	If just one or more of the turn signals are inoperative, refer to the Turn Signal Circuit Test.

⇒	If the turn signal indicators are inoperative, refer to Turn Signal Indicators Inoperative

2. If all turn signals operate as specified, but the trailer turn signal lamps are inoperative, refer to Trailer Turn Signal Lamps Inoperative.

All Turn Signals Inoperative

1. Ignition OFF, disconnect the X201 inline harness connector.
2. Install a 3A fused jumper wire between the B+ circuit terminal D5 and the ignition circuit terminal C5.
3. Ignition ON, verify that a test lamp illuminates between ignition circuit terminal A2 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

4. Ignition OFF, connect the X201 inline harness connector and disconnect the harness connector turn signal hazard flasher module.
5. Test for less than 1.0 ohm between ground circuit terminal 5 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

6. Ignition ON, verify that a test lamp illuminates between the control circuit terminal 2 and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the turn signal multifunction switch.

7. Connect a 10A fused jumper wire between the control circuit terminal 2 and the control circuit terminal 4.
8. Command the left turn signal ON using the turn signal multifunction switch. The left turn signal should illuminate.

⇒	If the left turn signal does not illuminate, test the control circuit terminal 4 for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the turn signal multifunction switch.

9. If all circuits test normal, replace the turn signal hazard flasher module.

Turn Signal Circuit Test

1. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
2. Test for less than 1.0 ohm between the appropriate ground circuit terminal listed below and ground.

•	Left or right front turn signal lamp terminal B

•	Left or right rear turn signal lamp terminal E

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

•	Left or right front turn signal lamp terminal A

•	Left or right rear turn signal lamp terminal C

4. Ignition ON, command the appropriate turn signal ON using the turn signal multifunction switch. The test lamp should flash ON and OFF.

⇒	If the test lamp is ON but does not flash ON and OFF, replace the turn signal hazard flasher module.

⇒	If the test lamp is always OFF, test the control circuit for a short ground or an open/high resistance. If the circuit tests normal, test or replace the turn signal multifunction switch.

5. If all circuits test normal, test or replace the turn signal bulb or the lamp assembly.

Turn Signal Indicators Inoperative

1. Ignition OFF, disconnect the harness connector at the instrument panel cluster (IPC).
2. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

•	Left turn signal indicator terminal A10

•	Right turn signal indicator terminal A7

3. Ignition ON, activate the appropriate turn signal. The test lamp should cycle ON and OFF.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance.

4. If the circuit tests normal, replace the IPC.

Trailer Turn Signal Lamps Inoperative

1. Ignition OFF, disconnect the appropriate LT or RT TRN TRLR Relay from the I/P - 2 fuse Block.
2. Test for less than 5.0 ohms between the ground circuit terminal 86 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, very that a test lamp does not illuminate between the control circuit terminal 30 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

4. Verify that a test lamp illuminates between the B+ circuit terminal 87 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Connect a test lamp between the control circuit terminal 85 and ground
6. Ignition ON, command the appropriate turn signal ON using the turn signal/multifunction switch. The test lamp should flash ON and OFF.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance.

7. Test for less than 5.0 ohms between the tractor/trailer receptacle ground circuit terminal B and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

8. Connect a test lamp between the appropriate control circuit terminal listed below and ground.

•	Left turn signal control circuit terminal G (C4/C5)

•	Right turn signal control circuit terminal D (C4/C5)

•	Left turn signal control circuit terminal 3 (C6/C7/C8)

•	Right turn signal control circuit terminal 5 (C6/C7/C8)

9. Connect a 10A fused jumper wire between the B+ circuit terminal 87 and the control circuit terminal 30. Verify the test lamp illuminates.

⇒	If the test lamp does not illuminate, test the control circuit for an open/high resistance.

10. If all circuits test normal, test or replace the trailer turn signal relay.

Turn Signal/Multifunction Switch

1. Ignition OFF, disconnect the X201 harness connector at the turn signal multifunction switch.
2. With the switch in the Active position, test for less than 1.0 ohm between control circuit terminal A2 and control circuit terminal A3.

⇒	If greater than the specified range, replace the turn signal multifunction switch.

3. With the switch in the Inactive position, test for infinite resistance between the control circuit terminal A2 and the control circuit terminal A3.

⇒	If less than the specified range, replace the turn signal multifunction switch.

Relay

1. Ignition OFF, disconnect the relay.
2. Test for 70-100 ohms between terminals 86 and 85.

⇒	If the resistance is not within the specified range, replace the appropriate relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 10A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 5.0 ohms between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.