Here's how to troubleshoot the problem:
1. Identify the Specific Fuse: Your owner's manual will show you which fuse controls the rear lights and number plate. Make absolutely sure you're replacing the *correct* fuse.
2. Visual Inspection (Caution!): With the fuse removed, carefully examine the wiring harness near the rear lights and number plate. Look for:
* Damaged Wires: Check for any fraying, exposed wires, or wires that are touching metal parts of the car (this is a common cause of shorts). Pay close attention to areas where the wiring might rub against the car body or other components.
* Corrosion: Look for corrosion on the connectors or wiring. This can cause a poor connection, leading to high current draw and a blown fuse.
* Damaged Bulbs: A faulty bulb with a short circuit can also blow the fuse. Examine the bulbs for damage or incorrect fitment.
* Water Ingress: Check for any signs of water intrusion into the rear light clusters or wiring harness. Water can cause corrosion and shorts.
3. Testing with a Multimeter (Optional but Recommended): If you're comfortable using a multimeter, this will help pinpoint the short. You'll need to:
* Set the multimeter to continuity testing (usually a diode symbol).
* Disconnect the wiring harness to the tail lights. This isolates the circuit.
* Test the continuity between the relevant wires in the harness (refer to a wiring diagram for your Ford Focus model year). You should *not* have continuity unless there is a short. If you *do* have continuity when the wires should be isolated, you have found the short.
* Repeat this process for the number plate light circuit.
4. Professional Help: If you cannot find the short circuit yourself after a thorough inspection, take your car to a qualified auto electrician or mechanic. They have the tools and expertise to diagnose and repair the problem safely.
Important Safety Precautions:
* Disconnect the battery negative terminal before doing any wiring inspection or testing. This will prevent accidental shocks or short circuits.
* Never work on electrical systems with the ignition on.
* If you're unsure about any part of this process, don't attempt it yourself. Seek professional help.
Ignoring a persistent blown fuse can lead to serious consequences. It's crucial to identify and fix the underlying short circuit to prevent further damage and ensure the safety of your vehicle and yourself.
