Tail Lights

Tail Lights (TL) — Troubleshooting Guide (SKU Group)

Important: Use this guide if you reinstalled your repaired (Tail Light) and the problem is still happening.
Important: Please do not open/disassemble the tail light assembly or probe/force connector pins (terminal damage can cause new faults).

• Step 1: Confirm exactly what’s failing
  • Identify which function is out: brake, turn, running/park, reverse, or cargo/CHMSL.
  • Confirm if it’s one side only or both sides, and if it’s intermittent (bumps/rain/wash).
• Step 2: Quick visual checks (most common causes)
  • Inspect the connector for water intrusion, green corrosion, loose pins, or a broken lock tab.
  • Check the harness where it flexes near the tailgate/bed for rubbed-through or stretched wiring.
• Step 3: Verify power and ground at the tail light connector
  • With lights commanded ON, confirm battery voltage is present on the correct pin for the failed function.
  • Confirm the ground pin can carry load (best test: use a test light from power to ground and verify it lights bright).
  • If voltage is present but dim/unstable, suspect high resistance in the connector or ground point.
• Step 4: Check fuses and related circuits
  • Check vehicle fuses for STOP, TURN, PARK/LAMP, REV, and TRAILER (names vary).
  • If a trailer harness is installed, inspect it for shorts/water—trailer wiring is a frequent cause of repeated tail lamp issues.
• Step 5: Check for BCM/lighting control issues
  • If multiple rear lighting functions act up, scan for BCM/body codes.
  • Confirm the vehicle isn’t reporting a bulb-out condition, short-to-ground, or open-load fault.
• Step 6: Rule out the bulb/harness side (if applicable)
  • If your version uses replaceable bulbs, verify correct bulb type and clean contacts.
  • Swap left/right bulbs (if possible) to see if the issue follows the bulb or stays with the vehicle side.
• Step 7: Intermittent-only issues
  • Lightly wiggle the connector and harness while the lights are ON (watch for flicker).
  • If symptoms change with movement, the most likely cause is connector pin fitment or broken wire inside insulation.
• Step 8: If everything tests good but it still fails
  • The issue is most likely vehicle-side: BCM output, ground distribution, connector/terminal fitment, or harness damage.
  • A local shop can do a loaded voltage-drop test end-to-end to pinpoint the exact high-resistance point.