Schematic Reference: Exterior Lights Schematics

Did you review the stop lamps operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Lighting Systems

1. Probe the stop lamp circuit of the tractor trailer receptacle with a test lamp that is connected to a good ground.
2. Press down the brake pedal.

Does the test lamp illuminate?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

1. Disconnect the trailer stop relay.
2. Probe the switch side voltage input circuit of the trailer stop relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 8

1. Probe the coil side control circuit of the trailer stop relay with a test lamp that is connected to a good ground,
2. Press down the brake pedal.

Does the test lamp illuminate?

Go to Step 5

Go to Step 9

1. Connect a test lamp between the coil side control circuit of the trailer stop relay and the coil side ground circuit of the trailer stop relay.
2. Press down the brake pedal.

Does the test lamp illuminate?

Go to Step 6

Go to Step 10

1. Connect a fused jumper wire between the switch side voltage input circuit of the trailer stop relay and the switch side output circuit of the trailer stop relay.
2. Probe the stop lamp circuit of the tractor trailer receptacle with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 11

Inspect for poor connections at the trailer stop relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

Repair an open, high resistance, or short to ground in the switch side voltage supply circuit of the trailer stop relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

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Repair an open, high resistance, or short to ground in the coil side control circuit of the trailer stop relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

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Repair an open or high resistance in the coil side ground circuit of the trailer stop relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

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Repair an open, high resistance, or short to ground in the stop lamp circuit of the tractor trailer receptacle. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

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Replace the trailer stop relay.

Did you complete the replacement?

Go to Step 13

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Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3