Dash cam installation in Lakemba

How a dash cam is fitted decides whether it is any use. Powered from the lighter socket you get a cable hanging across the dash, no socket left for a charger, and a camera that dies the moment the ignition goes off, which is exactly when the car is most likely to be hit.

Hardwiring means the power comes from the fuse box, via the right fuse tap and an inline fuse, and the lead goes up the A-pillar and along the headlining out of sight. The finished job looks like the camera came with the car.

It is the same careful trim removal we do for detailing work, which matters more than it sounds. Pillar trim on a modern car sits over curtain airbags, and clips break if they are levered rather than released.

Parking mode depends on it too. Without a permanent live feed from the fuse box the camera cannot stay awake while the car is parked, so a socket-powered camera never has parking mode at all, whatever the box says.

Resolution matters less than people assume past a point. What decides whether footage is useful in a claim is whether a number plate is legible, and that depends on frame rate, lens quality and how the camera handles glare far more than on the headline megapixel figure.

Sydney conditions are unkind to cheap sensors. Low winter sun straight down an east-west street, and the jump from bright daylight into a dark car park, are exactly the moments a poor camera blows out and loses the plate.

Position matters too. Behind the mirror, high on the glass, inside the swept area of the wipers. Mounted low on the dash it films the bonnet and a lot of sky reflection.

Dash cams write continuously and overwrite the oldest footage, which is an unusually punishing job for a memory card. A standard card will fail at it, often silently, and you find out when you need the footage.

Use a high-endurance card rated for continuous video, and format it in the camera every month or two. Most cameras have the option in the menu.

Check the camera is actually recording from time to time. A card that has failed frequently leaves the camera looking perfectly normal from the driver’s seat.

Older cars are simpler and harder at the same time. The fuse box is often easy to get at and the trim comes off without a fight, but the fuse layout is not always documented and there may be no obvious circuit that is live only with the ignition.

We test with a meter rather than guess, find the right ignition-switched and constant-live circuits, and tap them properly. On a car with a glass-fuse box the tap is different again.

An older car is also more likely to have a tired battery, which matters for parking mode. We check it, and if the battery is marginal we will say so before setting a cutoff that leaves you stranded.

Most cameras now download to your phone over their own Wi-Fi, which works but is slow for a long clip. For anything you need for a claim, take the card out and copy it to a computer, then put it back and format it.

GPS records where the car was and how fast it was going, stamped on the footage. That is useful for proving you were where you said, and worth remembering that it also records how fast you were going.

Some cameras store an event clip separately when they detect an impact, which stops it being overwritten. Find out where yours puts them before you need to.