Melbourne Rain, Storms and Your Car’s Electrics

Melbourne is known for weather that can swing from sun to downpour and back in an afternoon. This guide is for drivers who want their wipers, lights and wiring to cope with that, and for anyone whose car has started acting strangely after heavy rain, a flooded street or a hailstorm.

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Why changeable weather is hard on car electrics

Steady rain is not the main problem for a car's wiring. The trouble comes from the swings. A car heats up on a warm afternoon, then a cold change and a downpour cool everything quickly. Air inside light housings, connector shells and switch boxes contracts and pulls in moist air. Do that often enough and water collects in places it was never meant to be.

Melbourne also gets short, heavy bursts of rain from thunderstorms, mostly in the warmer months. Gutters and low streets can flood in minutes, and a car driven through even shallow water throws spray up into the engine bay and under the body, where many connectors and earth points sit.

Storms Melbourne remembers

Two storms show how quickly things can turn. On 6 March 2010, severe thunderstorms moved through the city from early afternoon and on into the eastern suburbs. The Bureau of Meteorology's March 2010 Victorian summary reports hailstones of up to 10 cm around Ferntree Gully, with widespread flash flooding and water damage across the CBD and the eastern suburbs. Insurers received tens of thousands of claims, and a great many cars were hail damaged.

On Christmas Day 2011, thunderstorms again brought large hail and significant property damage to Melbourne. The Bureau's December 2011 summary notes high rainfall totals the next morning, including 71.0 mm at Bundoora.

Most storms are nowhere near that severe, but the lesson is the same. Melbourne weather can go from harmless to damaging in well under an hour, so it pays to have wipers, lights and demisting working before you need them.

Wipers: the first thing to fail in a downpour

Wiper blades harden and crack in summer sun, then smear badly in the first heavy rain of the season. Replace them when they streak, chatter or leave a band of water across your view. That is a cheap fix with a big safety payoff.

If the wipers slow down, stop in odd places, or only work on some speeds, the problem is usually electrical or mechanical rather than the blades. Common causes include a blown fuse, a failing wiper relay, a worn motor, a faulty park switch inside the motor, or a seized linkage that makes the motor work too hard. Check the fuse first using our guide on how to check and replace a fuse. A fuse that blows again soon after replacement points to a seized linkage or a short, which needs proper diagnosis.

Many newer cars use rain sensors behind the windscreen to run the wipers automatically. A cracked or replaced windscreen, or a badly fitted sensor pad, can make them misbehave. That often needs recalibration rather than new parts.

Lights that fog up or fail in the wet

A little mist inside a headlight after rain can clear on its own once the lights warm up. Pooled water, or condensation that never clears, means the seal or vent has failed. Water in a headlight shortens globe life, corrodes the socket and can damage the reflector.

Tail lights suffer too, especially on older cars where the rubber seal has gone hard. Water sits in the bottom of the housing and slowly eats away the globe holder and the earth contact. Symptoms include dim lights, lights that work only when you tap the housing, or indicators that suddenly flash fast. Our guide on why indicators flash fast explains why a poor earth or failed globe causes that.

In heavy rain, make sure your headlights are on, not just daytime running lights. On many cars the tail lights are not lit with DRLs alone, which makes you hard to see from behind in spray.

Connectors, earths and the engine bay

Water and electricity meet most often at connectors. Plugs on sensors, the alternator, the starter and fans are usually sealed when new, but seals harden with heat and age. Once water gets in, the pins start to corrode. The result can be intermittent faults that only show up on wet days, such as a check engine light, rough running or a warning that clears itself once things dry out.

Earth points are another weak spot. A single corroded earth strap can cause dim lights, a slow crank and strange gauge readings all at once. If faults come and go with the weather, ask your auto electrician to check earths and connectors with the car wet, or to recreate the conditions with a careful spray of water. Reading stored fault codes helps narrow it down. See how to read fault codes with an OBD2 scanner.

Fogged windows and the demister circuit

When the weather turns cold and wet, windows fog fast. Your air conditioning is your best tool. Running it with the fan on the windscreen setting dries the air and clears fog far quicker than the fan alone. If the air conditioning is not working, have it checked. Any work on the refrigerant side must be done by a licensed technician.

The rear demister is a simple heating element printed on the glass, but it fails more often than people expect. A scratched line on the glass, a lifted connector tab at the edge of the window, a failed relay or a blown fuse will stop it working. If only some lines clear, look for a break in those lines.

After a flood, hailstorm or deep water

If you have driven through water deeper than the bottom of the doors, or the car was parked in floodwater, don't keep starting it to see if it works. Water in the engine can cause serious mechanical damage, and water in wiring and modules can cause faults that appear weeks later. Have it inspected first, and talk to your insurer.

Hail damage is mostly panel and glass work, but check the electrical side too. Broken lenses let water into lights. Cracked windscreens can upset rain sensors and camera-based safety systems. A smashed sunroof or a leaking seal can let water reach the wiring and modules that sit under carpets or in the roof lining.

• Check every light, inside and out, for water or flicker.
• Test wipers on every speed and the washers.
• Look under the carpets and in the boot for damp patches.
• Watch for new warning lights over the following days.
• Smell for burning or hot plastic. If you notice either, stop and get it checked.

Getting help

Wet-weather faults are often intermittent, so write down when they happen and what the weather was doing. That saves diagnosis time. If you are in the inner suburbs or the hills where the 2010 hail hit hardest, our pages for Inner Melbourne and the Maroondah and Yarra Ranges list local auto electricians.

Parts for this job

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Get it done: get a quoteDo it yourself: shop wiper blades

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Get it done: get a quoteDo it yourself: shop waterproof connectors

Get it done: get a quoteDo it yourself: shop relays

Questions Melbourne drivers ask

Why do my car's electrical faults only show up when it rains?

Usually water is getting into a connector, an earth point or a light housing whose seal has aged. When it is dry the contact works. When it is wet, moisture and corrosion add resistance or cause a short. An auto electrician can track it down by inspecting connectors and earths, reading fault codes and, if needed, recreating wet conditions carefully.

Is condensation inside my headlight a problem?

A light mist that clears once the lights have been on for a while is common. Water pooling in the bottom, or fog that never clears, means a failed seal or blocked vent. Left alone, it shortens globe life and corrodes the socket and reflector. Resealing may work, but a badly affected headlight often needs replacing.

My wipers stopped mid-screen in a downpour. What's wrong?

Check the wiper fuse first. If it is fine, the likely causes are a failed relay, a faulty park switch in the motor, a worn motor or a seized linkage. A fuse that keeps blowing usually points to the linkage or a short. Drive carefully to a safe place and get it checked, since driving in heavy rain without wipers is dangerous.

Should I start my car after it has been in floodwater?

No. If water got above the floor or near the air intake, starting the engine could cause serious mechanical damage, and wet modules and wiring may short. Leave it switched off, contact your insurer and have it inspected. Faults from flood damage can take weeks to appear, so get it properly checked even if it seems fine.

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