I replaced the bulbs and fuses on my 08 Ford Expedition but my reverse lights are still not working?

Principles of Operation
The transmission control module (TCM) sends gear status information to the PCM over the communication network. When the transmission is in REVERSE (R), the TCM energizes a relay which supplies voltage to the reversing lamps.

Could be a bad relay . But testing an not guessing is the way to a fix . Looking at wiring diagrams an using a DVOM - digital volt ohmmeter to test electrical circuits is . Also hooking up a scan tool an checking for codes .

Inspection and Verification

1. Verify the customer concern.

1. Visually inspect the following for obvious signs of electrical damage.

Visual Inspection Chart Electrical

• Battery junction box (BJB) fuse 33 (20A)
• Transmission control module (TCM)
• Bulb(s)
• Circuitry

1. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.

1. NOTE: Make sure to use the latest scan tool software release. If the cause is not visually evident, connect the scan tool to the data link connector (DLC).

1. NOTE: The vehicle communication module (VCM) LED prove-out confirms power and ground from the DLC are provided to the VCM. If the scan tool does not communicate with the VCM:
   • Check the VCM connection to the vehicle.
   • Check the scan tool connection to the VCM.
   • Refer to Section 418-00 , No Power To The Scan Tool, to diagnose no communication with the scan tool.

1. If the scan tool does not communicate with the vehicle:
   • Verify the ignition key is in the ON position.
   • Verify the scan tool operation with a known good vehicle.
   • Refer to Section 418-00 to diagnose no response from the powertrain control module (PCM).

1. Carry out the network test.
   • If the scan tool responds with no communication for one or more modules, refer to Section 418-00 .
   • If the network test passes, retrieve and record the continuous memory DTCs.

1. Clear the continuous DTCs and carry out the self-test diagnostics for the TCM.

1. If the DTCs retrieved are related to the concern, refer to the Transmission Control Module (TCM) Diagnostic Trouble Code (DTC) Chart. For all other DTCs, refer to Section 419-10 .

1. If no DTCs related to the concern are retrieved, GO to Symptom Chart .

Transmission Control Module (TCM) Diagnostic Trouble Code (DTC) Chart DTC Description Action P1910 Reverse Lamp Control Circuit/Open Go To Pinpoint Test U . P1911 Reverse Lamp Control Circuit Low Go To Pinpoint Test U . P1912 Reverse Lamp Control Circuit High Go To Pinpoint Test U . All other DTCs - REFER to Section 307-01A or Section 307-01B .

• The reversing lamps are inoperative

• Fuse
• Circuitry
• Battery junction box (BJB)
• Reversing lamp relay
• Transmission control module (TCM)

• Go To Pinpoint Test U .

Also having ford factory service repair manual helps

Pinpoint Test U: The Reversing Lamps Are Inoperative
Refer to Wiring Diagrams Cell 93 , Reversing Lamps for schematic and connector information.
Normal Operation Voltage is supplied from the battery junction box (BJB) fuse 33 (20A) to the switched side of the reversing lamps relay. The reversing lamps relay coil power is supplied by the transmission control module (TCM) (also called a main control valve body for Expedition and a mechatronic assembly for Navigator) through circuit CAT03 (GY/BN). The reversing lamps relay coil ground is controlled by the TCM through circuit RET24 (BN/BU). When the reversing lamps relay is energized, voltage is routed to the reversing lamps through circuit CLS10 (GN/BN).
DTC P1910 - sets when the TCM detects an open from the reversing lamps relay coil voltage supply circuit.
DTC P1911 - sets when the TCM detects a short to ground from the reversing lamps relay coil voltage supply circuit.
DTC P1912 - sets when the TCM detects a short to voltage from the reversing lamps relay coil voltage supply circuit.

Possible Causes
• Fuse
• Circuit CAT03 (GY/BN) open, short to ground or voltage
• Circuit CLS10 (GN/BN) open
• Circuit RET24 (BN/BU) open
• Reversing lamps relay
• BJB
• TCM

You might need to make sure that the reverse switch is sending a 12v signal to the backup lamps.