# Taillights not always on with headlights?



## Reid (Apr 25, 2018)

I was driving in the rain yesterday, and came across another 3 with no taillights. Visibility was a bit poor, so I glanced down at my screen, curious as to why the other car's lights weren't on. My headlights were showing as on. But then later when I passed that car, I noticed their headlights (and foglights) were, in fact, on! 

I noticed a few other 3s in the same state on my drive -- which led me to the conclusion that, even though my car was telling me my lights were on, it was probably that my taillights were completely out! 

I'm not sure if there's a difference between "lights on because wipers are on" (CA law now, and likely the software on most cars triggers auto headlights with wipers by now)... or if it's some kind of "low light but not night" state... Regardless, I find it surprising that there's a mode where the headlights are on but the taillights are not. I'm not sure why this would be desirable. 

Can't find anything on this topic via a search. Anyone know more detail about what causes this state?


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## BluestarE3 (Oct 12, 2017)

Yes, the highlights do come on automatically when the wipers are in operation. This is also mentioned in the owner's manual, but it doesn't say anything about the taillights. I've always assumed the taillights come on with the headlights, but now you've piqued my curiosity. When it starts raining here again, I may have to check it out.


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## MelindaV (Apr 2, 2016)

Reid said:


> I was driving in the rain yesterday, and came across another 3 with no taillights. Visibility was a bit poor, so I glanced down at my screen, curious as to why the other car's lights weren't on. My headlights were showing as on. But then later when I passed that car, I noticed their headlights (and foglights) were, in fact, on!
> 
> I noticed a few other 3s in the same state on my drive -- which led me to the conclusion that, even though my car was telling me my lights were on, it was probably that my taillights were completely out!
> 
> ...


I think what you saw on the other car were the signature lights, not the actual headlights.


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## Reid (Apr 25, 2018)

MelindaV said:


> I think what you saw on the other car were the signature lights, not the actual headlights.


No, that's incorrect. It was my first thought as well, of course. I verified that the other car's headlights were, in fact, on, as were the foglights. As I noted, it would have also been weird for my auto headlights to be on but theirs off. I also found the same thing on at least one other model 3 (and I was back and forth enough in traffic to check the same car headlight vs taillight multiple times).


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## gary in NY (Dec 2, 2018)

Another example of weird taillight behavior: We were discussing in another tread a while back that when you leave the car, and have the headlights set to stay on after exit, the taillights do not stay lit. This is concerning to me because when I get out to check my mailbox after dark, it's very hard to see the car from behind. I have not found a way to override this. I'd like not to be rear-ended while checking the mail.


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## BluestarE3 (Oct 12, 2017)

gary in NY said:


> Another example of weird taillight behavior: We were discussing in another tread a while back that when you leave the car, and have the headlights set to stay on after exit, the taillights do not stay lit. This is concerning to me because when I get out to check my mailbox after dark, it's very hard to see the car from behind. I have not found a way to override this. I'd like not to be rear-ended while checking the mail.


I remember that thread; however, with my car, both the headlights and taillights remain illuminated after exiting and closing the door (that's with "Headlights After Exit" enabled): https://teslaownersonline.com/threads/keep-headlights-on.10550/#post-190700

If there's indeed variability in taillight behavior for "Headlights After Exit" from car to car, maybe there's similar variability in taillight behavior when lights turn on automatically with the wipers?


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## processengr (Aug 17, 2017)

gary in NY said:


> Another example of weird taillight behavior: We were discussing in another tread a while back that when you leave the car, and have the headlights set to stay on after exit, the taillights do not stay lit. This is concerning to me because when I get out to check my mailbox after dark, it's very hard to see the car from behind. I have not found a way to override this. I'd like not to be rear-ended while checking the mail.


Mine does the same thing...


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## Common_Loon (Jan 21, 2019)

Is it possible to submit this as a bug report to Tesla? This seems an insane and sloppy oversight.


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## BluestarE3 (Oct 12, 2017)

Common_Loon said:


> Is it possible to submit this as a bug report to Tesla? This seems an insane and sloppy oversight.


Has anyone been able to replicate the scenario described by the OP?


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## Guest (Feb 5, 2019)

Modern vehicles (at least in EU) are required to have DRL. But requirement (unfortunately) doesn't require rear tails to be lit in daytime.
BMW and many other reasonable car manufacturers chose to activate them with DRLs (no license plate lights).
It's safe to drive with unlit tails but lights must be kept in AUTO mode. When it gets dark, low beams switch on (with license and tail lights) automatically.


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## sola scientia (Sep 24, 2018)

Only an hour ago, there I was, tootling along the 401, in the dark, snow flying, me with no running lights. Other cars were trying to draw my attention to the situation, but since I can't tell the difference between someone flashing their lights in anger, or in concern, or which car they are trying to notify, it took me until I got home to realize the horrible truth.

But after playing around, I now understand what happened.

If you are sitting in the stopped car, googling something or whatever, out of respect for some business or house in front of you, you naturally turn off the headlights -- "exterior lights off". As far as I know, its the only way to turn off the headlights.

When you drive away, the headlights snap back on. Such convenience! You feel "problem solved". Unfortunately, this convenience comes at a big price: when the headlights snap on, the runners do not come on. (I encourage readers to test this.)

My sense is that, when exterior lights are "off", either the headlights should not automatically snap on when the car is shifted into "D" (this would warn/remind the driver of the 'off' setting he made), or, when the headlights are turned on automatically, so should the runners.

The simplest fix is almost certainly the latter -- I'll guess either adding or changing a single line of code would do it. It is also consistent with existing behavior when you get into a parked car, or if you turn the car on by pressing the brake.

Nevertheless, I think the former would be better in the end. Take that "exterior lights" control and split it up: one for each kind of light, and the control would be "off, on, auto" setting.


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## iChris93 (Feb 3, 2017)

sola scientia said:


> When you drive away, the headlights snap back on. Such convenience! You feel "problem solved". Unfortunately, this convenience comes at a big price: when the headlights snap on, the runners do not come on. (I encourage readers to test this.)
> 
> My sense is that, when exterior lights are "off", either the headlights should not automatically snap on when the car is shifted into "D" (this would warn/remind the driver of the 'off' setting he made), or, when the headlights are turned on automatically, so should the runners.


I'm pretty certain that only the DRL come on when you drive off. I know because I have turned my lights off when waiting to pick someone up. When driving off, I could tell some light was on but it was not bright enough to be my low beams so I had to go to the menu to turn them on. I think a good solution would be having auto turn back on when going into drive.


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## Magnets! (Jan 10, 2019)

On a similar note, I double parked briefly tonight and wanted to leave parking lights on for visibility, so I selected that option, closed the door and out they go, no lights. What is the purpose of parking lights if you can't park with them on?


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## sola scientia (Sep 24, 2018)

iChris93 said:


> I'm pretty certain that only the DRL come on when you drive off. I know because I have turned my lights off when waiting to pick someone up. When driving off, I could tell some light was on but it was not bright enough to be my low beams so I had to go to the menu to turn them on. I think a good solution would be having auto turn back on when going into drive.


For my Model 3, there is a difference between "off" and "auto" while the car is in drive ("D"). However, the difference is about 1/4 photographic stop according to one of my cameras. When the lights come on in the "off" state, its basically as usable as in the "auto". You'd only notice in an A/B comparison.

This is in contrast to another (non-Tesla) car I tested: there was at least a two photographic stop difference (~factor of 4) between daytime running lights and full headlights. Trivially noticeable.

Whatever the actual ratio is, I agree with your solution -- flip it back to "auto", for full-power headlights, with running/tail lights. I've sent a note to Tesla about this.


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## Guest (Mar 4, 2019)

AFAIK, legally, DRL must be on if no other light is activated and vehicle is being driven.
If low beams or parking lights are activated, DRLs shall not be active.
Often DRL and front parking lights are the same thing though luminosity requirements are different and NOT overlapping. 
Almost all European cars support always on parking lights. Some even support ONE-SIDE parking lights (to save power, activate
only the side - closer to traffic.


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## iChris93 (Feb 3, 2017)

arnis said:


> AFAIK, legally, DRL must be on if no other light is activated and vehicle is being driven.
> If low beams or parking lights are activated, DRLs shall not be active.


Depends on jurisdiction.


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