# Diagnosis: If a car headlight doesn't work on low-beam... **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 11, 2016, 7:06pm UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847 "2016-02-11T19:06:24Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 12, 2016, 5:19pm UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/21 "2016-02-12T17:19:05Z")
> [@Doctor\_Jackson](#): > > Also, it’s a given that, should you follow my instructions above step by step, your car will be different and you’ll screw something up. 😃 Yeah, you might forget to disconnect and reconnect the electrical plug for the bulb. 😃 😃 ---
**Author:** ![Bruce\_Wayne](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@Bruce\_Wayne](https://boards.straightdope.com/u/Bruce_Wayne)\ **Post date:** [February 12, 2016, 5:48pm UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/22 "2016-02-12T17:48:57Z")
> [@Paintcharge](#): > > Does the car only have one bulb for both high and low? That’s the way most cars are now. The bulb has two filaments, high beams and low beams, and the one for low has blown. You need a new bulb. I second this. ---
**Author:** ![Doctor\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doctor_jackson/32/32_2.png) [@Doctor\_Jackson](https://boards.straightdope.com/u/Doctor_Jackson)\ **Post date:** [February 12, 2016, 9:35pm UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/23 "2016-02-12T21:35:15Z")
> [@Really\_Not\_All\_That\_Bright](#): > > IME, the plastic ring and rubber boot are generally part of one assembly, and the bulb and its socket come out with the ring. The first part is also a pretty common arrangement, but I wasn’t writing a Chilton’s manual;) . The second part is certainly possible, but I have not seen it. > [@Gary\_T](#): > > Yeah, you might forget to disconnect and reconnect the electrical plug for the bulb. 😃 😃 Steps 4 & 5, unless my brain is cramping and you mean something else that I’m not thinking of. If the former is the case, then :p, if the latter :o ---
**Author:** ![Iggy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iggy/32/3364_2.png) [@Iggy](https://boards.straightdope.com/u/Iggy)\ **Post date:** [February 13, 2016, 12:14am UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/24 "2016-02-13T00:14:03Z")
I’ve been having the same issue with my 2000 Mitsubishi Pajero iO. But I suspect it is a problem in the fuse box as a few other electrical problems arose at the same time as the headlight problem and those seem to run on fuses at are adjacent to the headlamp fuse. Sigh. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [February 13, 2016, 2:56am UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/25 "2016-02-13T02:56:52Z")
> [@Doctor\_Jackson](#): > > The first part is also a pretty common arrangement, but I wasn’t writing a Chilton’s manual;) . Does Chilton still publish? We had them at the library where I worked, I was able to fix a fellow employee’s car after a former boyfriend ripped the cables off of her distributor…a Dodge Charger, as I recall…but I digress. I haven’t seen a Chilton in some time, absolutely no automobile schematics. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 14, 2016, 5:15am UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/26 "2016-02-14T05:15:20Z")
> [@Doctor\_Jackson](#): > > It’s certainly not rocket science, but simple does not necessarily equal easy. The general steps for most modern cars are: > > 1. If present, remove any rubber boot (these keep moisture out of the back of the headlight assembly). Note the orientation of the boot for reassembly. > 2. Remove the back of the headlight assembly (generally involves unscrewing a plastic ring) and slide it out of the way. > 3. Reach inside the assembly, usually where one cannot see, and determine the type of retaining system for the bulb. This usually involves a spring clip where one either squeezes the ends together or pushes the head of the clip back and to the left to release. Fortunately the clips are almost always attached to the assembly on one side and swing out of the way, so you don’t have to worry about losing the clip. If lucky it won’t involve clips but will be a twist lock set up where you twist the bulb harness until the tabs line up and slide it out. These are, to me, the easiest to remove/replace and therefore are the least common. > 4. Unplug the old bulb > 5. Plug the new bulb firmly into the wiring harness, paying attention to the warnings about about not touching the glass. I wrap the glass part in a thick, clean shop rag to make sure I don’t accidentally touch it while pushing the bulb into the plug. Thick paper towels work as well. Gloves can work, but they must be clean. > 6. At this point I turn on the headlights to make sure the bulb is working properly. > 7. Carefully insert the new bulb into the headlight assembly, making sure it seats completely (doesn’t move around when you jiggle the harness). For this step you cannot use the rag/towel/glove to protect the glass from your skin oils, so be careful to handle by the harness. > 8. Reverse steps 1-3 to reassemble > [@Gary\_T](#): > > Yeah, you might forget to disconnect and reconnect the electrical plug for the bulb. 😃 😃 > [@Doctor\_Jackson](#): > > Steps 4 & 5, unless my brain is cramping and you mean something else that I’m not thinking of. If the former is the case, then :p, if the latter :o Then you’re out of sequence. On designs where the electrical plug is exposed, disconnecting it should be step one. On designs where the plug is inaccessible until a cover is removed, removing said cover is step one and disconnecting the plug is step two. You don’t want to be doing the steps 1,2, & 3 you’ve listed with the plug still connected. ---
**Author:** ![Doctor\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doctor_jackson/32/32_2.png) [@Doctor\_Jackson](https://boards.straightdope.com/u/Doctor_Jackson)\ **Post date:** [February 15, 2016, 2:23pm UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/27 "2016-02-15T14:23:14Z")
> [@carnivorousplant](#): > > Does Chilton still publish? We had them at the library where I worked, I was able to fix a fellow employee’s car after a former boyfriend ripped the cables off of her distributor…a Dodge Charger, as I recall…but I digress. I haven’t seen a Chilton in some time, absolutely no automobile schematics. They [absolutely](http://www.chiltondiy.com/) do! To be honest, though, Haynes is the more available choice around here. > [@Gary\_T](#): > > Then you’re out of sequence. On designs where the electrical plug is exposed, disconnecting it should be step one. On designs where the plug is inaccessible until a cover is removed, removing said cover is step one and disconnecting the plug is step two. You don’t want to be doing the steps 1,2, & 3 you’ve listed with the plug still connected. Hmm, it works in my mind and I just replaced bulbs on my wife’s (Tucson) and Daughter’s (CR-V) vehicles. I guess we’ll just have to agree that I’m a lousy tech writer! ---
**Author:** ![inscrutable](https://avatars.discourse-cdn.com/v4/letter/i/a88e4f/32.png) [@inscrutable](https://boards.straightdope.com/u/inscrutable)\ **Post date:** [February 15, 2016, 3:21pm UTC](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847/28 "2016-02-15T15:21:23Z")
Some cars (like Saab) have a relay that controls headlight operation. Make sure the relay is making good contact in its socket, if it doesn’t need replacing. [Previous page](https://boards.straightdope.com/t/diagnosis-if-a-car-headlight-doesnt-work-on-low-beam/745847.md?page=1)