2019 Ram 1500: Diagnosing and Repairing Broken Wire for No License Plate Lights

Initial Diagnosis and Customer Complaint

• 💡 A customer brought in a 2019 Ram 1500 with a complaint of no license plate lights, despite replacing the factory LED bulbs.
• ⚠️ The truck also had codes related to the headlight switch, fog lights, and center stop lamp, but the primary focus was the license plate lights.
• 🔍 The technician noted that the license plate lights were the only factory LED bulbs on the entire truck, with all other bulbs being incandescent.

Electrical System and Wiring Challenges

• 🧠 The body control module (BCM) has a driver for the license plate lights, and the diagnostic trouble code (DTC) indicated a short circuit to battery or open circuit.
• 🗺️ Difficulty was encountered in obtaining accurate wiring diagrams, with service data and aftermarket diagrams proving unreliable, lacking crucial connector details.
• 🕵️‍♂️ A visual inspection revealed signs of previous tampering and connectors that were not properly secured.

Locating the Broken Wire

• 📍 The technician traced the wiring harness, suspecting a splice point (SL3) where the circuit splits to the left and right plate lamps.
• ⚡ By using a power probe and live data, the technician confirmed the BCM was attempting to activate the license plate lights.
• 🔍 After extensive probing and testing, a broken wire was suspected in the harness, likely due to corrosion or physical damage, specifically a white wire with dark blue stripe.

Repair Strategy: Overlay Harness

• 🛠️ Due to the inaccessibility of the harness section (pinched between the body and frame, or near the fuel tank), a direct repair was deemed impractical.
• 💡 The most feasible solution identified was to perform an overlay harness repair, running a new wire to bypass the damaged section.
• ⚠️ This decision was made in consultation with the customer, prioritizing a practical repair over extensive disassembly.

Overlay Installation and Testing

• 🧵 An 18-gauge white wire was used for the overlay, routed alongside the factory harness and secured with zip ties and tape.
• ✅ The new wire was connected to the existing harness, and the license plate lights were tested using the scan tool, confirming functionality.
• 🧐 A secondary issue with the headlight switch was noted but not addressed, as it was outside the scope of the initial repair request.

Final Assessment and Conclusion

• 🏆 Despite the challenges and the decision to perform an overlay, the license plate lights were successfully repaired.
• 🤔 The technician expressed a preference for traditional repairs but acknowledged the necessity of the overlay in this specific situation.
• 🔧 The repair involved soldering and heat-shrinking the new wire connection, with attention paid to securing the harness to prevent future issues.