Replacing the bulbs in your car tail lights with LEDs

Recently I went through the process of replacing most of the incandescent bulbs in my car with LEDs.  Why did I do this?  Mostly because it reduces the risk of someone tail-ending my car. led-bulb

Many new cars these days, especially the more expensive cars, use LED bulbs almost exclusively instead of traditional incandescent bulbs.  But my car is just old enough, and just inexpensive enough, that all of the tail lights, brake lights, turn signal lights, and running lights are old-fashioned incandescent bulbs.

Why do we care about this?

The chief reason we care about this is that when you tap the brake pedal of your car, it closes an electrical switch that sends an electric current through your brake lights.  The tungsten filaments heat up, and about one-tenth of a second later, the brake lights light up.

If only you were to replace the incandescent bulbs with LED bulbs, the brake lights would light up instantly.

How far does the car behind you, speeding along at 70 miles per hour, travel in a tenth of a second?  Turns out, about ten feet.  So if you swap out your incandescent brake lights for LEDs, you might avoid some car accident where some inattentive driver behind you rear-ends your car.  You give the inattentive driver behind you an extra ten feet to react to the situation.

There is also a physiology-of-perception aspect to this.  It turns out that the human visual cortex is optimized to detect the first derivative (calculus again!) of the brightness of things.  A brake light that lights up instantly is more noticed by the visual cortex than a brake light that gradually changes from off to on over a tenth of a second, because the first derivative is higher in magnitude.  Look at a few car brake lights the next time you are driving around and you will see this for yourself.  You can immediately pick out the cars that have LED brake lights.  It’s just much more noticeable than incandescent brake lights.

Okay so hopefully I have convinced you to swap out those bulbs.

If you are going to go to the trouble to do this, you might as well also swap out as many other bulbs as you can.  Turn signals, running lights, tail lights, all of them.  The way I did this was by studying the user manual for my car and writing down all of the bulb types.  And then I went to Amazon and ordered up LED equivalents. Note carefully that some bulbs are red and some are yellow.

Yes you could go to your local auto parts store to try to find these LED bulbs.  When I tried that, I found that no single store had all of the bulbs I needed, and even traveling around to three different local stores, I was not able to find them all.  Mail order is the way to go, I think.  Plus it was cheaper at Amazon.

If you tackle this project, there are many things to watch out for.

A first problem is that with cars nowadays it can be really difficult to get at the various bulbs.  In my car, a Subaru, to get at the front turn signal bulbs I had to remove a front tire, remove a plastic fender liner, and reach up through the car body to unhook a socket that cannot be seen but can only be felt because it is around a corner.

A second problem is that the replacement LED bulb sometimes will not fit into the space where the old incandescent bulb sat.  A millimeter too large in this direction or that direction, that kind of thing.  For one spot in my car I had to order three different LED bulbs, each of which seemed identical to the others in terms of the catalog description, until by chance I found one that would fit.

A third problem is that your turn signal blinker is (intentionally) very sensitive to the amount of current drawn by the (incandescent) bulbs.  This is so that if you have a burned-out bulb the blinker will blink extra fast and this will tip you off that you need to find a burned-out bulb and replace it.  To use LEDs, you will have to replace the blinker module with one that blinks at a constant rate regardless of the current drawn.  In my car this module was in a place under the dash that could not be seen, and could only be felt, because it was around a corner.

If you tackle this project, when the time comes to actually unplug an old incandescent bulb and plug in the new LED bulb, here are a couple of tips.

First, be sure to smear a bunch of silicone goop into each socket before you plug in the new bulb.  The goop is hydrophobic and so it keeps stray moisture out of the socket and reduces the risk of corrosion and a bad electrical connection.  It keeps the metal surfaces unoxidized.

Second, recall that a tungsten filament does not at all care whether the electrons run through the filament this way or that way.  So the sockets are designed in a way that does not force you to orient the bulb in any particular direction.  LEDs in contrast are very picky about which direction the current flows.  This means that when you plug in the new LED bulb, there is a 50% chance the bulb will not light up.  If you picked wrong, you will need to unplug the LED bulb and plug it in the other way.

There are other benefits to swapping out the incandescent bulbs for LED bulbs.  For one thing, probably for the life of the car you will never need to worry again about having to replace a bulb.  And you will reduce the chances of getting pulled over by the police due to a burned-out tail light or whatever.

54 thoughts on “Replacing the bulbs in your car tail lights with LEDs

  1. Carl, very detailed information
    hope you remember me, I smiled at your reference to “physiology-of-perception aspect ”
    dee

  2. Be careful with LED brake lights, many of the LED replacements have an insignificant difference between just the marker (lights on, but not brakes on) and brakes on. It can be almost impossible to tell you have applied the brakes by the change in brightness. That is, needless to say, very dangerous when driving at night.

      • true. thats what im doing right now.
        led for 12 volts on brake lights and 9 volts for tail lights..and some bits of circuit..and nc / no relays.

    • Mine got the same issue, at night when pressing brake the light does not get brighter which is suppose to.. also, i change reverse light to LED and the reverse camera does not work properly.. and i guess thats it, my car is with incandesent forever since no one know the solution..

      • The LEDs do not draw enough current to signal to the camera that you are in reverse. Adding a resistor across the wires to the light that triggers your camera will fix this.

      • Put a resistor in line to fool the computer into thinking there is nothing wrong with the circuit. Currently the led lights draw so little current that the computer thinks the lights are not even on.

  3. “smear a bunch of silicone goop into each socket” What is this stuff never heard of it?

    Where do you get the flashy thingy?

    • Dialectric grease sold at any parts store not silicone, silicone will harden, dialectric grease won’t and it’s what auto manufacturers use.

  4. The “Silicone Goop” is called Dielectric. You get a little package of it when you change spark plugs and spark plug wires at the auto parts store. A small tube of it will last a long time. It should be put in every electrical connection on your car. This will prevent the green corrosion you sometimes encounter when you disconnect something on your car that hasn’t been opened in years. The atmosphere contains a certain amount of moisture all the time (Humidity). This moisture can condense when there is a change in temperature (Dew Point). It is like moisture running down the outside of a cold glass of sweet tea. Any electrical connection that air can get into then moisture can get in it, as well. Goop is a preventative measure to insure years of good electrical connections with out corrosion.

    • No, no, no, no, NO!!!!!
      Silicone should never be used on low voltage connections. Its a great way to cause horrible problems. When I have to fix siliconed connections, I replace them, cleaning it off is too hard. If you really must grease your connections, use contact grease. Dielectric grease is for plug leads only. They have enough voltage to blast through a thin layer of silicone.

      • Any insulative / dielectric grease can be used. Silicone is the best because it has a stupidly high heat rating (few hundreds of degrees) it also basically never evaporates.

        The Bulb leg (lead), and socket are quite capable of scraping away the grease in only the spot they touch, which negates this insulative properties of the grease. All greases are insulative. Silicone is thick, doesn’t dry out / crack (oxidize…easily), and conducts heat away from the bulb, and socket.

        It will prevent normal bulbs from roaching the socket. It will prevent corrosion. You can actually coat the whole bulb in a thick coating (the glass included), and it will keep the bulb from shattering if water gets past the housing.

        Wherever there is a little bit of grease, still on the asperities of the imperfectly polished metal, the electrons (virtual photons) will just tunnel through it.

        I can see the argument of grease-less connections for sensitive instruments where the insulator / dielectric / capacitor could throw off the reading. For automotive there isn’t a reason to not use it.

        I generally go with the Teflon / Silicone brake grease, since a whole tube is 5 bucks.

  5. I disagree. The cost of the LEDs, the difficulty in finding exact replacements, (Some are oversized), the new flasher module needed for them to work, the annoyance of removing lenses, batteries, air ducts, wires, etc and the fact that ordinary incandescent bulbs last years anyway makes this a worthless endeavor. Cost vs benefit does not show this to be a worthwhile action. In addition there are no real world studies to indicate LED lights on cars reduce accidents.

    the only benefit I see is if you leave the console light on all day and your battery dies. Less likely with LED as it draws less current.

    If something is working, leave it alone. unless you have idle time, and a burning need to throw money out.

    One could argue that side mirrors which blink when turn signals are put on are a safety consideration. Would you then spend hundreds on replacing side mirrors?

    A car is a sink hole. spend as little as possible, only when needed and put the rest of your money into savings.

    • Humm, while I agree with you in principal (I’ve driven my 4 cyl sports car for over 15 years), I disagree with you on this. LED lights cost a lot less than they have before. Since I have two marker lights out anyway, I’m going to replace these, all marker lights, third brake lights and license plate lights all with LEDS. This will take 30 minutes or less and the cost is negligible. Power is not free. In a 4 cyl you can feel it and you can see it on your RPM gauge when you hit all the lights for night time driving. The RPMs will slightly raise. This power from the alternator has to come from somewhere, it isn’t free! It will cost either in gas mileage or performance. Just by swapping out these BS lights (we’re not even talking about major lights) I’ll be saving 70 watts. That will show up in GM or performance. We certainly don’t need a studies for that, it’s a fact.

      • The alternator is only ~30-40% efficient as well, so for three bulbs (GM 4157, or similar) it uses 1/2 horsepower (35 watts x 3 = 105 Watts) divided by .3 = 315 watts.

        You can also dip the bulb in silicone sealant to waterproof it if it isn’t already, so no more blown bulbs.

        Also, live a little. Do something fun. The joy of making something better is certainly worth the dollar.

    • No the replacement module is designed to work with either incandescent or LED’s. Also, the module is only linked to your turn signal, therefore it has no effect on the other safety lights of the vehicle.

  6. I was impressed by the daytime safety difference the LED replacements made.
    Great if you only drive during the day.
    But I would not buy them because of the opposite effect at night time!
    Very little difference between the bright tail light on & the brake light applied!!

  7. I recently replace the brake lights with LEDs on a 1994 silverado and when i press the brake only the rear left brake blinks the weird part is when I press the brake the front left signal blinks as well!! Any answers ??

    • You need to flip the light your having problems with around leds are polarity sensitive sometimes when installing a different light I can change the polarity of the other one and cause it not to work

  8. Hello there, I wonder… can enyone tell me:
    Is that true, that a replacement of the incadescent headlight bulb fore a LED one might be illegal and my car will fail next MOT test- I’ve got a Corsa year 1999. I was told by a friend of mine- already after I’ve asked my car mechanic to do it. Now I feel stressed that I’ve done something wrong…
    Please any suggestions…
    Thank You

    • Yes, its an not failure. Headlights need a very small source of light to work correctly. LEDs are nowhere near that yet.

  9. Ops… it’s me again- sorry I have not noticed that this is not a UK site.
    I guess it might be a different law in USA about this bulb replacement -I do not know.
    I was so interested about the commments that i’ve missed it,

  10. Buyer beware of led tail bulbs from Wal mart total junk bought some for my car and after a week it fell apart and didn’t have any. Rear running lights on one side a friend told me about it part of the led bulb fell off. So I put the original incandesnt bulbs back in

  11. Led burn? In 4 days my led lights from america (made in china) burnt a hole through it’s self…..do all leds have this issue…i drive a 2013 cruze.

    • If you bought the same leds from Amazon as I did, then you too have been a victim of poor engineering.
      There is a small 31.4 ohm resistor inside the led lamp base. that resistor is supposed to drop the voltage
      from 12 volts down to around 8 volts. The 8 volts cause the tail light to appear dim when the brakes are
      applied (the brake light is fed the full 12 volts). The resistor does not have the power rating needed. It looks
      like a 1/8 watt unit. Trouble is that the 4.8 volts times the 0.152 A. flowing thru it generates over 3/4 of a watt
      of power. So the resistor heats up really fast and melts the socket. The brake and tail light are the same
      led lamp. That is what I have found. The led draws 0.298 A. when the brakes are applied.
      Good Luck.

  12. Well one and all, I have read all of your comments, I have just replaced all of the internal lights in my car, what a performance, like many of you finding the correct LED is hard enough then when you get it, it won’t fit, and I was sent some blue/white led’s and while the LED may not get hot the bulb holder was so hot I had to put it down a bit smartish
    Just found out something which is part of the MOT test, by law you are not allowed to replace or up grade any bulb other than what was fitted when the car was new, just thought you would like to know, ad for me, I’m going back to incadesents

  13. I think if that delay were enough to cause a crash you should perhaps ecourage the driver behind you to leave a longer gap, either by slamming on the brakes of slowing down when ever they get too close. I know that the circuit in the indicator light relay is set up to function at a certain amount of resistance/ current from each light if you change those to LED the rate at which your blinkers flash at will become faster.
    The New SMD LED lights generate a massive amount of heat that may not have the chance to disipate when used as rear lights for night driving and could be a fire hazard, as for using as brake lights in general might be OK.
    BTY not all high end new cars have LED brake lights, at least my wife’s doesn’t 2016 SUV, but it is optional.

  14. I just got replacement LED indicator bulbs for my car. Fitted them, they work with that nice LED sharpness but they are not very bright. It appears the bulb is shorter than the original non-LED bulb and doesn’t go as far into the recess as the old one. Any ideas how I can rectify this or do I need to buy longer bulbs!

  15. I noticed ALL the LED replacement bulbs at my auto parts store are marked
    For Off Road use ONLY. That would make then illegal for street use.

  16. The fraction of a second difference between when an led or incandescent bulb actually lights up really won’t help you much if any at all from a safety perspective as the comparatively long reaction time of a human is what gets you rear ended

    • Well, it sounds like under a typical example the car behind is able to stop 10 feet shorter.

      I would think this means an accident is avoided occasionally- when the car would otherwise would have barely rear-ended you.

      And in accidents that will still occur even with the quicker stopping time, the impact should be slightly less because the car behind will be going slightly slower upon impact with the LED than it would have with the incandescent.

      So yes I would expect that the benefit may be pretty modest, but it certainly can’t hurt.

  17. This makes a great point about using LED bulbs for tail light. I like that idea of having one less thing to worry about. Getting pulled over by a cop is no fun. I’ve heard that things like vehicle deceleration warning lamps can be useful for making your tail lights more noticeable as well.

  18. After having to replace burned out bulbs on my 2011 Kia Forte I was wondering whether LEDs are available and would avoid having to replace bulbs. Apparently so. The faster response time sounds like another good reason to have LEDs.

  19. Wow… lots of good information. However, I have one for you. 2001 Toyota Corolla. MOST lights changed to LED with no issues at all. New ‘blinker’ module installed. Works great. 1157 base brake lights… now comes the issue. I put the LED bulbs in, super bright, great differential between running light and brake light. Excellent swap. BUT, now the third brake light is acting like the outboard brake lights. Normal dimness (is that a word?) when in night mode. Bright brakelightiness (that needs to be a real word!!) when I stomp on the brake pedal. I was told it is illegal for the third light to be on all the time, even if it acts like the normal brake lights. It MUST be off when the brakes are not being applied. How do I fix this?

  20. I know this is old but could someone explain why my led brake lights aren’t that bright? They are 1157 and the tail lights and brake lights are the same bulb but when I press the brake there isn’t much difference in the tail light and brake light. Is there a reason for this or something I can do to fix that issue? The bulbs I have in there are supposed to be for that application

  21. Added LED’s to my 5×8 trailer, both brakes likes comes on, each turn signal comes on, but when applying brakes and a turn signal at the same time, left or right, the brake light for that particular turn signal goes out but the opposite side brake light still stays on. Is this a normal function of a LED?
    I also notice this behavior when I was behind a newer Silverado and his left turn signal was blinking, but had no brake lights on that side but the right break light was on. What replaces the stop filament on the incandescent bulb on to the LED

  22. I put led bulbs in my brake and turn front and back. My hazards work but turn signal doesnt flash. I put in a new flasher in for led and still doesnt work. What do i do

  23. I replaced all of the outside lights on my motorhome. I also replaced the flasher with a HD flasher that is “designed for LED and standard bulbs. My turn signals flash slowly with the engine running and will stop flashing with the engine off. I suspect I have another problem in the system but what?

  24. 2000 grand am. Changed the tail/ brake lights, two per side. All 4 tail lights work. When I press the brake only the left bulb on each side gets brighter. Does anyone have suggestion to try? Any help would be greatly appreciated.

  25. I have a 2013 Ford Focus and I have installed LED lights for the brake lights and they are working great overall, except when car is turned off the leds are staying slightly illuminated (not fully on but not all the way off) does anyone know why the lights are doing this? Or how to fix this issue?

  26. I have a 1973 VW karmann Ghia that I am in the process of changing bulbs to LED. I haven’t found a suitable Flasher / Hazard warning relay yet so that is on hold. Front LED sidelights work, no problem.I got correct bulbs for reversing lights and stop and tail lights but not working apart from stop light. Contacts on base of bulbs are touching contacts on lamp holder. . Have checked bulbs direct to battery and are OK. When I put original bulbs back every thing working. I have even run separate earths to bulbs but still not working. Any ideas or information would be appriciated

  27. A few things to think about.
    1. Modern cars often require extra load balancing resistors. CANBUS for example. Those resistors often cause high temperatures exceeding temperatures of a conventional bulb.
    2. LEDs are often very spotty and don’t evenly fill the reflector bucket.
    3. Driving around with insanely bright lights may improve your visibility while blinding others.

    I have tons of LED lights and some cars just can’t do them without proper knowledge. If I need to do too much, I just skip it. In my Fiat 500 Abarth for example, a major pain.

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