Rats, Possums and Chewed Car Wiring in Sydney

This guide is for Sydney drivers who've found droppings under the bonnet, a strange warning light or a car that won't start after a night parked near bushland. It explains why rodents chew wiring, which parts of Sydney see more of it, how to spot damage early, and how to get it repaired so it lasts.

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Why animals end up in your engine bay

An engine bay is warm after a drive, sheltered from rain and full of gaps to squeeze into. For a rat or mouse, that makes it a good place to rest or nest, especially on cool nights. Rats and mice have teeth that keep growing, so they gnaw on things to keep them worn down. Wiring insulation, plastic tubing and foam sound deadening are all within reach.

Possums are a different case. They mostly climb in for shelter, and the mess they leave behind (droppings, urine and nesting material) can cause as much trouble as chewing. Possums are protected in NSW, so don't try to trap or relocate one yourself. Sutherland Shire Council, for example, suggests contacting WIRES for a referral to a licensed possum handler.

The soy-based insulation question

You'll often read that newer cars are more at risk because some makers use plant-based materials, including soy, in wiring insulation. Be careful with this one. Some manufacturers have used soy-based materials in place of part of the petroleum-based plastic, but there's no solid evidence that this attracts rodents. In the United States, a class action against one large car maker over rodent damage was dismissed in 2018, partly because the animals had chewed both soy-based and conventional materials.

The practical takeaway is simple. Rodents damage cars of every age and brand. Don't assume an older car is safe or a newer one is doomed. Focus on what you can control: where the car sits, what's around it and how quickly you find damage.

Bushland-edge suburbs see more of it

Sydney has a lot of houses that back onto bush. Around Hornsby and the Hills, suburbs border bushland and national parks such as Berowra Valley and Ku-ring-gai Chase. On the Northern Beaches, Garigal and Ku-ring-gai Chase national parks run close to homes. In the Sutherland Shire, the Royal National Park sits on the doorstep. Native animals, rats and mice all move between bush, backyards and garages.

It's not only a bush problem. Inner-city laneways, older terraces with gaps under the floors, and anywhere with bins, compost or pet food nearby can draw rats too. Cars that sit for a week or more, such as a second car, a caravan tow vehicle or a work ute over the holidays, are the most likely targets.

Signs your car has had visitors

Damage often shows up as an electrical fault that seems to come from nowhere. A quick look under the bonnet can save hours of diagnosis later. Our national guide on rodent damage to car wiring covers the general checks. Here's what Sydney drivers commonly report:

• Droppings, leaves, chewed foam or shredded paper on top of the engine or battery.
• Bite marks on wiring, plastic covers or the bonnet insulation pad.
• A sudden warning light, or several at once, after the car has been parked.
• A car that cranks but won't start, or won't crank at all.
• A burning or musty smell when the engine warms up.
• Gauges, lights or the air conditioning fan cutting in and out.

Deterrents that are worth trying

No deterrent works every time, so use a few together. Start with the area around the car. Keep bins sealed, move pet food and bird seed away from the garage, and trim back plants touching the car. If you park in a garage, look for gaps where animals get in.

Under the bonnet, you can wrap exposed sections of loom in tough split conduit or rodent-resistant tape, and some owners fit mesh over openings. Opening the bonnet every few days, or simply driving the car more often, also helps because animals prefer quiet spots. Avoid baits in the engine bay. A poisoned animal can die somewhere you can't reach, and baits are a risk to pets and native wildlife.

If rats keep coming back, a licensed pest controller can deal with the source. For possums, contact WIRES or a licensed handler rather than acting yourself.

Insurance: check before you book the repair

Whether animal damage is covered depends on your policy. Some comprehensive policies cover it and some exclude it, and an excess usually applies. Read your product disclosure statement, call your insurer before work starts, and take photos of the droppings and chewed wiring. Ask the repairer to keep the damaged section and write up what they found, as the insurer may want it.

Why chewed wiring needs proper joins

It's tempting to twist the wires together and wrap them in tape. Don't. Twisted joins work loose and corrode, and on a modern car many wires carry low-voltage sensor or network signals that a poor join will upset. A fix that seems fine in the driveway can cause an intermittent fault months later.

A good repair uses the same size wire, a quality crimped or soldered join, and adhesive-lined heat shrink to seal out moisture. Joins should be staggered so the loom doesn't end up with a lump in one spot. Our guides on crimping wire connectors and cable sizing for 12 V explain the basics.

If the damage is near airbag wiring, high-voltage cabling on a hybrid or EV, or a data network loom, leave it to a professional. Sometimes a section of loom or a sensor connector has to be replaced. An auto electrician can also scan for stored fault codes after the repair to make sure nothing was missed.

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Questions Sydney drivers ask

Do soy-based wires attract rats?

It's often claimed, but it hasn't been proven. Some car makers have used soy-based materials in wiring insulation, yet rodents also chew conventional plastic insulation and other materials. A US class action on the issue was dismissed in 2018. Treat every car as a possible target and focus on deterrents and early checks.

What should I do if a possum is living in my car?

Don't trap or handle it. Possums are protected in NSW. Leave the bonnet open in daylight with lights on, as they prefer dark, quiet places, and contact WIRES for advice or a referral to a licensed possum handler. Once it's gone, check the wiring and clean out droppings and nesting material.

Can I fix chewed wires myself?

Simple damage to a power or lighting wire can be repaired with the right size wire, crimped or soldered joins and sealed heat shrink. Leave it to a professional if the damage is in an airbag circuit, a sensor or network loom, or near high-voltage hybrid or EV cabling. Twisted wires and tape aren't a proper repair.

Will my insurance cover rodent damage?

It depends on your policy. Some comprehensive policies cover animal damage and others exclude it, and an excess often applies. Check your product disclosure statement, call your insurer before starting repairs and keep photos and the damaged section of wiring as evidence.

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