Why were car headlights ever designed to stay on when the key's removed?
November 30, 2015 12:03 PM   Subscribe

This seems to be changing somewhat these days. I see a lot of models these days that shut them off, but still every day I get messages from an admin at work telling people that their lights are on in the parking lot. This has been killing batteries for nearly a century now. Is there a good reason for what seems to be a design flaw?
posted by basehead to Technology (18 answers total) 2 users marked this as a favorite
Some cars have a 'coming home' feature that leaves the headlights (DRLs maybe?) on for a minute or so after you lock the doors, illuminating your surroundings as you walk into your house at night.

However the greater culprit in lighting misadventures seems to be cars that have always-on DRLs and always-on dash lights, where there's no visual cue in daytime whether your headlights are actually on or not. But many cars douse the headlamps when the ignition is off, and just run parking lights.
posted by a halcyon day at 12:15 PM on November 30, 2015

Ever gotten together with a dozen of your friends in the middle of nowhere to drink beers and didn't want to light a fire? You park in a circle and leave the headlights on.

Ever needed to run back into the house for a minute to grab your wallet? You leave the headlights on so you can see better to open the front door.

There are other reasons, but basically it boils down to people maybe wanting their headlights to stay on every now and then, so it's easier to make that possible and engineer around the possibility of leaving them on accidentally (e.g., a chime whenever the car is turned off and the lights are still on).
posted by Etrigan at 12:16 PM on November 30, 2015 [10 favorites]

Sort of what Etrigan says: it gives agency to the owner. I would also think that it's not a design flaw but a usage flaw.
posted by Namlit at 12:21 PM on November 30, 2015 [1 favorite]

I'm sort of thinking people driving with lights on during the day is a fairly recent habit. I'm late 40s and it was not taught that in my drivers ed and I only started doing probably in the last ten years. So in the beginning people only drove with with them on when it was dark, i.e., when you could tell they were on and would think to turn them off.

One of my favorite George Carlin bits was the one about him wanting to run into people who drove with lights on during the day to prove that it wasn't safer. Contrary old bastard that he was.
posted by Beti at 12:34 PM on November 30, 2015 [1 favorite]

I'm sort of thinking people driving with lights on during the day is a fairly recent habit. I'm late 40s and it was not taught that in my drivers ed and I only started doing probably in the last ten years. So in the beginning people only drove with with them on when it was dark, i.e., when you could tell they were on and would think to turn them off.

Even in the days before daytime running lights* became a thing, people would often start their commutes in darkness and forget that their lights were on by the time they got to work. That's what leads to office notifications of "If you drive a blue Corolla, your lights are on."

* -- Either in the form of automatic DRLs or just people turning their headlights on during the day, which I agree has become more popular recently.
posted by Etrigan at 12:46 PM on November 30, 2015 [1 favorite]

Not sure, but maybe simpler wiring? Headlights have a pretty big current draw, and its probably easier (or cheaper) to run them off the battery bus than the switched bus.
posted by hwyengr at 1:09 PM on November 30, 2015 [1 favorite]

As a data point, my 1989 Subaru Justy had headlights that turned off with the key and I thought it was awesome. Since then, I've had three different vehicles which stopped dinging at me when forgetting the headlights on, which has resulted in multiple accidental leavings-on, and I remember how excellent the Justy was: it was impossible to leave the headlights on.

But, one problem we did have, when it was cold: If I left the lights on, then turned the car off, when turning it on with a cold battery the headlights used so much current that the car had difficulty starting until you turned the headlights off. In theory, this is the same with the usual non-switched lights, which means if you leave them on the car doesn't start at all, so I don't know how good an argument that is.

My solution would be a timer -- you need to turn them back on every 2 minutes -- or a low-voltage meter that shuts off extraneous electronics if the voltage drops below the level that would turn the starter.
posted by AzraelBrown at 1:31 PM on November 30, 2015

Why were car headlights ever designed to stay on when the key's removed?

The first cars had gas powered headlights and many early cars that had electric lights the lights were an extra cost option (in as much as anything was standard at that time). So it wasn't that they were designed seperate as much as they were seperate or installed later.

Once lights became standard the draw of the lights was much higher than the switched ignition components. Because the contacts required were so much larger it made sense to keep them discrete from the ignition switch.

And there were other reasons to enable lights to come on independent of the engine running state. EG: turning your lights on was how you called for car hops.

But mainly automotive electrics live a very hard life. They are exposed to vibrations, extremes of heat and cold, extremes of humidity; and all sorts of harsh chemicals. Engineers had to spend a lot of time getting them reliable (not always successfully *Cough* Lucas *Cough*) and any sort of integration with other functions is/was troublesome. Keeping things separate was easier and more reliable. This has only recently changed with microprocessor control of car systems. Even then it is often advantageous, for example, to have components be vacuum actuated rather than electric.
posted by Mitheral at 2:09 PM on November 30, 2015 [4 favorites]

This weirdly seems to vary from brand to brand. As AzraelBrown said, subarus have had the auto-off feature for ages(and my dad uses it like DRLs, he just leaves the lights in the "on" position all the time knowing the key will shut them off). Whereas my partners 05 nissan has them stay on.

Weirdly the trend seems to be that budget american brands and hyundai and such have auto-off, but the basic models from toyota/nissan/etc don't. I feel like my friends 80s merc 190e had auto-off as well.

Personally i think the biggest problem is the cars with lights that stay on for a couple minutes or 30 seconds or whatever. You ALWAYS get some heart in the right place dingleberry going "OMG you forgot to turn your lights off!" and sometimes they don't believe you. Jeep has had that "feature" since the late 80s or early 90s. It bugs me to have to put the key in to turn the lights on in the subaru, but the lights staying on even with the switch off just feels inherently wrong.
posted by emptythought at 2:10 PM on November 30, 2015 [1 favorite]

I bought my current vehicle, used, from this Hungarian dude who'd been doing all the mechanical maintenance himself. First time I took it in for an oil change/general inspection, my mechanic noticed that he had rewired it so that the engine doesn't shut off until the lights do - I can turn the key and remove it, but the diesel engine just keeps chugging along until I click the light switch. Without my saying anything, he immediately asked if the previous owner was by chance from Eastern Europe - said he's seen that a handful of times and it's always been in vehicles owned by Eastern Europe immigrants.

He offered to switch it back to default for me (apparently there's a greater risk of battery draw leaks this way) but I opted to keep it. 3 years later, no battery issues, but it's definitely saved me from leaving the lights on at least 15-20 times.
posted by mannequito at 4:09 PM on November 30, 2015 [3 favorites]

Newer cars are supposed to have a feature where, if the car isn't running and the battery is draining, it will turn everything off while it still has enough charge to start the car.
posted by VTX at 5:54 PM on November 30, 2015

Subaru's headlights turn off when you shut off the car... unless you press a button to keep them on... I hate when my wife drives my car because she turns my lights off by default - and I just exit the car.
posted by Nanukthedog at 6:10 PM on November 30, 2015

Before the driver's station trunk release was invented, you often needed the keys for the trunk. Sometimes you wanted the lights to stay on while you did that.

I hate the feature where they stay on for some time and then turn themselves off. It was my military training for so long it's habit now: don't trust things to do what they're supposed to if you can help it. Start a pump, check to make sure the motor's humming, water is moving, and system temperatures are doing what they should. Add chemicals to the boiler, sample again afterwards to make sure the expected thing happened. I shut my garage door, I watch it shut. I don't walk away assuming it's going to finish up by itself. I've been burned by a feature like that before assuming the dome light would turn off. Turned out I had somehow switched it from "turn off after a while" to "always on" without knowing it. So when I rent a car with this feature, I find myself impatiently waiting where I can see the car until the lights go off.

But I still want the ability to turn them on without leaving my keys in the ignition just in case I ever wanted to do that. I can't think of why I'd want to do that, but a car that would not let me if I wanted would feel insulting. I like the ones with off/auto/on so I can override what the car wants either way.
posted by ctmf at 7:44 PM on November 30, 2015 [1 favorite]

All my 1960s air-cooled Volkswagens had headlights that stayed on without the ignition. (Up to 1966, these were still 6-volt systems with very aenemic headlights and easily drained batteries.) Also, contrary to today's (US) standards, the radio (if so-equipped) also worked without the keys -- but the horn did not.

However, my father's 1971 VW's headlights did turn off with the ignition switch -- as did the horn, while the radio still did not require they key.

I believe VW made this change to ignition switched headlights on all models after 1970. I don't know at what point they reversed the decision that people might want to listen to the radio but would never need the horn when the ignition is off, but my 1988 GTI had the now-conventional set-up: headlights and radio require ignition key, horn does not.

I think these and other variations represent individual engineering decisions by individual makes, depending on the available technology of the day, what could be marketed to the consumer, and what represented the lowest cost and maintenance (vs user habits, which are, essentially, free). See also Mitheral's answer for the historical technical details.

Nowadays, however, with cheap and robust digital technology, the cheapest cars can now automate these things and run everything through the ignition switch.
posted by Herodios at 8:36 PM on November 30, 2015

Nerdy VW anecdata: Lights on my '73 Type 3 are independent of the ignition, with no chime to announce that they're on. It's a 12V car, but the electric routing may not be original.
posted by a halcyon day at 9:15 PM on November 30, 2015

VW Anecdata, my '72 super had lights independent of the key.
posted by plinth at 2:48 AM on December 1, 2015

Early cars had a simple, 2 position ignition switch: On and Off. When the switch was in the On position, the engine ignition system was hot and if the ignition points were in the closed position (edit: with the engine not running) you could burn the contact points and burnt points are bad for engine performance.

That is why auxiliary electric circuits such as lights would work when the ignition was Off. More sophisticated, 3 position ignition switches were later developed that had Off, On and ACCessory positions. Selected electrical circuits (usually radio, at least) would work in the ACC position without a current flow to the ignition system
posted by buggzzee23 at 4:21 AM on December 1, 2015

As an addendum to my above post, it should be noted that modern cars have electronic ignition systems that operate without the old, electromechanical ignition points.
posted by buggzzee23 at 4:34 AM on December 1, 2015

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