# Automotive puzzler **URL:** \ **Category:** Factual Questions\ **Created:** [May 29, 2021, 9:23pm UTC](https://boards.straightdope.com/t/automotive-puzzler/943188 "2021-05-29T21:23:47Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![jaycat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jaycat/32/3015_2.png) [@jaycat](https://boards.straightdope.com/u/jaycat)\ **Post date:** [May 29, 2021, 9:23pm UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/1 "2021-05-29T21:23:47Z")
'13 Toyota Corolla, 66,000 miles … out of the blue, when I turn on my headlights, the display lights on the radio and clock go almost completely dim. Any thoughts on this phenomenon? Thanks! ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [May 29, 2021, 9:30pm UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/2 "2021-05-29T21:30:05Z")
That sounds like a feature. Headlights means its nighttime, which means you need less light to see the dash and you don’t want to be blinded by the dash. ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [May 29, 2021, 9:42pm UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/3 "2021-05-29T21:42:00Z")
Agreed. Look for a dial that will increase the brightness of the dashboard lights when the headlights are on. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [May 29, 2021, 9:46pm UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/4 "2021-05-29T21:46:42Z")
As stated above, modern cars dim the dash lights when the headlights are on. If they’re a lot dimmer than they used to be, the first thing I would check is the dimmer switch. I know from experience that it’s possible to accidentally change the setting. See page 151 of the [owner’s manual](https://www.toyota.com/t3Portal/document/om-s/OM12E11U/pdf/OM12E11U.pdf) (large PDF) for the location. If that’s not it, then other possible causes are a bad battery, bad battery connection, or bad alternator. ---
**Author:** ![jaycat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jaycat/32/3015_2.png) [@jaycat](https://boards.straightdope.com/u/jaycat)\ **Post date:** [May 29, 2021, 10:03pm UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/5 "2021-05-29T22:03:22Z")
> [@bibliophage](#): > > As stated above, modern cars dim the dash lights when the headlights are on. If they’re a lot dimmer than they used to be, the first thing I would check is the dimmer switch. I know from experience that it’s possible to accidentally change the setting. See page 151 of the [owner’s manual](https://www.toyota.com/t3Portal/document/om-s/OM12E11U/pdf/OM12E11U.pdf) (large PDF) for the location. If that’s not it, then other possible causes are a bad battery, bad battery connection, or bad alternator Many thanks for researching that. I just went out and checked and I think you guys must be right, it’s just funny I never noticed it before. Today was a grey rainy day so I had the headlights on and thought it odd I couldn’t see the clock or radio display at all. Now that it’s starting to get dark, they are visible, just dim. BTW, that little knob (which is also the odometer reset) only dims the instrument panel, not the clock and the radio. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [May 30, 2021, 3:27am UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/6 "2021-05-30T03:27:39Z")
On my '19 Subaru Forester there’s a dimmer to adjust the dash illumination. But it’s not controlled by the headlamp switch. There’s a sensor on the dash that dims the illumination based on the outside the car brightness. If the headlamps are on and it’s bright outside the dash stays bright. ---
**Author:** ![WildaBeast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wildabeast/32/6_2.png) [@WildaBeast](https://boards.straightdope.com/u/WildaBeast)\ **Post date:** [May 30, 2021, 5:16am UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/7 "2021-05-30T05:16:22Z")
This isn’t a new feature by any means. I remember my parents’ '84 Voyager doing the same thing when I was a kid. ---
**Author:** ![tavaritz](https://avatars.discourse-cdn.com/v4/letter/t/71e660/32.png) [@tavaritz](https://boards.straightdope.com/u/tavaritz)\ **Post date:** [May 30, 2021, 6:49am UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/8 "2021-05-30T06:49:21Z")
Probably for European market. Here you have to have your headlights on all the time. It’s not for the driver to see better but for others to see the car. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [May 30, 2021, 7:54am UTC](https://boards.straightdope.com/t/automotive-puzzler/943188/9 "2021-05-30T07:54:51Z")
You might want to check if the sensor is somehow blocked. That might make it overly eager to dim the dashboard in medium light when the headlights are on. That might have made the transition more obvious.