Ever Noticed The Wires Behind Your Rear View Mirror? Here's What They're For

There's no getting around the fact that modern cars are more sophisticated and tech-laden than ever. Even the most basic, entry-level new cars now come standard with tech features that were hardly imaginable on a luxury car just 15 or 20 years ago. A now ubiquitous feature, like adaptive cruise control, is a good example of how prevalent some of this tech has become. 

Though it's easy to hop in the driver's seat without any thought to it, the number of sensors and components and the amount of wiring hidden beneath a car's surface can be daunting. And sometimes you'll notice this in places that might be unexpected, like your car's rear-view mirror.

Depending on the age and type of your vehicle, you may have noticed at some point, maybe while cleaning your dashboard or washing your windshield, that there are wires coming out of your rear-view mirror. Even if you haven't seen the wires themselves, there's a good chance they're lurking just beneath those plastic covers. So what exactly are these wires, and what do they do? While it can vary greatly from car to car, the wiring is typically there for auto-dimming capability, compasses, connected safety services, or HomeLink garage door openers.

The rear-view mirror is one of the simplest and most effective safety features in the history of the auto industry. And for a long time, mirrors were simply that — a mirror that could be positioned and adjusted for the driver's height and seating position as a way to see through the rear window.

But beginning in the late '80s and into the '90s, rear-view mirrors started to become more than a basic mirrored panel. In 1982, a company called Gentex developed the world's first auto-dimming mirror, and for the 1988 model year, the Lincoln Continental could be had with one of these groundbreaking new auto-dimming mirrors. Soon, the feature began to spread not just to other automakers, but to less expensive vehicles as well.

Auto-dimming mirrors are electrochromic and function by using sensors and a microprocessor to detect glare and effectively tint or clear the mirror as needed. And as you'd imagine, an auto-dimming mirror will need a power source, and therefore, wiring to function. The system can usually be engaged manually as well, and that's one of the big reasons why you'll often see a power button on your rear-view mirror.

Beyond auto-dimming, there are other possible rear-view mirror features that necessitate wiring. A compass display is a common feature on modern cars, and a lot of rear-view mirrors include buttons to access emergency and roadside assistance. The most commonly pressed buttons on a rear-view mirror, though, will likely be programmable HomeLink buttons to open or close your garage door or gate. Depending on the automaker, these buttons aren't always on the mirror itself, but it's the most common location for them.

If you have an older vehicle, or if your car's mirror lacks some of these features from the factory, you can easily add an aftermarket mirror with auto-dimming or HomeLink functionality, though you'll of course have to add the wiring as part of the install. 

As we are starting to see with both factory and aftermarket options, some physical mirrors themselves are starting to be replaced by digital rear-view monitors that display an image from a rear-facing camera. To take things even further, the new Polestar 4 didn't just do away with its physical rear-view mirror;  Polestar got rid of its whole rear window altogether, the driver's back view replaced entirely with a rear-facing camera display. If you thought the wires were strange, how's that for being tech-laden?