Ford Fuse Box Repair

Ford Central Junction Box (CJB) / Fuse Box – Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired Ford Central Junction Box (CJB) and the problem is still happening.
Important: Please do not open/disassemble the fuse box—check fuses, relays, power/grounds, and wiring first.

• Step 1: Confirm installation
  • Verify the CJB is fully mounted and every connector is fully seated/locked
  • Inspect connector pins for bent/pushed pins, corrosion, or looseness
  • Make sure the harness isn’t pulled tight or pinched (intermittent issues are common from tension)
• Step 2: Battery, charging, and main grounds
  • Confirm the battery is fully charged and passes a load test
  • Clean/tighten battery terminals and engine/chassis grounds
  • Low voltage or poor grounds can cause relay chatter, random stalls, and intermittent accessories
• Step 3: Re-check fuses and relays correctly
  • Confirm the correct fuses are installed in the correct locations (no “close enough” fuse swaps)
  • Test fuses for power on both sides (key OFF / key ON where applicable)
  • Swap known-good relays for any related circuits (fuel pump, ignition, horn, battery saver, PCM power, etc.)
• Step 4: If you have “No start / Hard start”
  • Determine which condition you have:
    • No crank: focus on starter relay circuit, ignition switch, neutral safety/PRNDL, and grounds
    • Crank/no start: confirm fuel pressure and scan for engine codes before blaming the CJB
  • Check for intermittent loss of power to PCM/engine controls during crank
• Step 5: If the vehicle stalls intermittently
  • Watch for voltage drop or power loss events at the CJB power feeds during the stall
  • Inspect for loose battery cables, failing grounds, or worn ignition switch (very common)
  • Check for aftermarket wiring (remote start, lights, audio) tied into ignition/accessory circuits
• Step 6: If “Battery saver relay” issues are suspected
  • Confirm doors/ajar switches aren’t falsely reporting “door open” (keeps modules awake)
  • Check for stuck relays or relay control problems caused by low voltage or poor grounds
  • Verify interior lighting/courtesy circuits aren’t shorted or backfeeding
• Step 7: If the horn is intermittent or inoperative
  • Verify the horn itself works (power/ground test at the horn)
  • Check the horn relay and the relay socket terminals for looseness/heat damage
  • Inspect steering wheel switch/clockspring circuits if the relay never gets commanded
• Step 8: Check for water intrusion and connector damage
  • Inspect for moisture under the dash / kick panel area and signs of water tracks
  • Check for green corrosion, swollen terminals, or evidence of prior handling/service at connectors
• Course of action
  • If the issue persists, contact UpFix with your VIN, full code list, and whether it’s no crank vs crank/no start vs stall so we can help narrow it down. Call or email for assistance.