Headlights, an electric window or the power socket suddenly stopped working? Before heading to an auto electrician, look in the fuse box. A blown fuse is not a sign of poor quality: it did its job and protected more expensive electronics.
The under-bonnet fuse box lives next to a hot engine, moisture and the road salt thrown up in winter. Corroded contacts cause faults that look like serious failures. Maintenance is simple and takes half an hour.
What you will need
Important: Before starting, switch off the ignition, remove the key and turn off all electrical loads. Never fit a fuse of a higher rating than specified and never bridge it with wire: it can cause a fire.
Step 1
Find the fuse box and the layout
Most cars have two fuse boxes: one under the bonnet and one inside, under or beside the dashboard. The layout and ratings are in the handbook or on the inside of the lid.
Remove the lid and inspect the box for water, dirt or signs of melted plastic.
Step 2
Check that fuses are correctly fitted
Compare each fuse with the layout: the amp rating and position must match exactly. A wrong rating or a fuse in the wrong slot may blow or fail to protect the circuit.
Pull out the fuse for the dead circuit with the puller and look at the link through the clear body. A broken link means replacing it with a new fuse of the same rating.
Step 3
Clean the contacts
Shake the can of WD-40 Specialist Contact Cleaner and spray the sockets and fuse legs from 15-30 cm away. It dissolves dirt and oxidation, displaces condensation and restores conductivity.
Let it dry completely before turning on the ignition. Do not start the engine until the product has fully evaporated.
Step 4
Protect against moisture and corrosion
Once the cleaner has dried, give the box a light mist of WD-40 Multi-Use: it displaces moisture and leaves a thin film that slows corrosion. The WD-40 Smart Straw makes precise application easy.
Check the lid seal and close it firmly so water and dust stay out.
Step 5
Test and find the cause
Turn on the ignition and check the circuit that was not working. If a new fuse blows again straight away, there is a short circuit or a faulty component on that circuit.
In that case do not fit a higher-rated fuse; take the car to an auto electrician.
Tip: Keep a set of spare fuses in common ratings in the glovebox: a blown wiper or headlight fuse on a wet winter night can be replaced in a minute at the roadside.
What next
Inspect and clean the fuse box every autumn before the salt season and after an engine wash. While you are at it, treat the battery terminals and main under-bonnet connectors with Contact Cleaner too.
These uses come from the experience of WD-40 users in many countries. Always follow the instructions and warnings on the product label.
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