Driving at night with LED DRL

MX-5 2016+ with LED DRL looks very stylish, however, DRL will turn off if the headlights are enabled. Some people would prefer they stay on all the time. Here is a long discussion on the Miata forum. 

DRL and headlight are controlled by an ESU module, which is located next to the dead pedal, under the steel plate.


Wiring diagram



Conditions for DRLs



ESU cover plate

Even though this could be easily modified by adding a relay, the location of these wires makes it very difficult. A few people asked me if I can provide an easier solution.

I had a spare ESU module from a salvage car, which was very helpful in selecting the proper connectors. I was able to source a male/female connector to construct wire harness with modification to enable DRL when headlights are on.

I think the main reason why DRL is turning off during the night is their brightness; it will create more distractions for oncoming traffic. To avoid this, brightness must be reduced at night.  This could be a bit challenging. DRL LED unit has an internal analog current control circuit, which will provide constant light output (at 670mA LED current) at a wide range of input voltage.


LED DRL regulator

After experimenting with the test unit, I discovered that if the voltage drops below 8V, it is no longer regulated. At 7V, brightness is about 50% (300mA LED current)  of the normal one. This can be easily achieved simply by adding 20 Ohm/10W resistor for one unit, or 10 Ohm for both. Using two diodes and one resistor we can get switchable DRL with day/night mode. Together with a 5″ harness, I have a complete Plug-n-Play solution.

DRL harness

First prototype

To install this harness, it will be necessary to remove the metal protective plate first. This plate is attached by two 10mm nuts. Unfortunately, one nut is under the Styrofoam panel…

Next step is to unplug 10 pin connector from the ESU unit


ESU with DRL connector unplugged

Insert my harness and put everything back.


Installed harness

Now DRL will stay on with reduced brightness when headlights are on.

These harnesses are available for ordering through my store.

26 thoughts on “Driving at night with LED DRL

  1. Thanks for another great product & post, Sergey!
    Question: AFAIK there are two DRLs – one is the vertical DRL on the bottom, and the other is the little light in the headlight unit itself, on the inside edge (closer to the emblem) –
    do you know how/if we can make those stay on as well?


    • These corner lights are marker lights, connected with side and tail markers, They are on when headlights are on or you can turn them on by light switch, anytime.


  2. Pingback: My MX-5 … DRL Harness by MX5 Things – Life Beyond Politics

  3. Hi Sergey, do you think it’s possible to do this, but opposite, for the rear running lights (The red LED bars that go around the indicators) so that they come on at all times with the DRL, instead of only when the marker/headlights are on?

    It would work well with your new rear lightbar too.


      • actually , I was wrong, it is same cable. So it is possible.

        Correction: it is possible only for front markers. Tail light markers powered from other two connectors, so two additional harness will be neccessory


    • I have new solution for the front marker lights, but rear markers powered from two separate connectors. To activate them with DRL we will need 3 harnesses, which will be expensive solution.


    • Your rear lights or are not lit when driving with DRL? In Europe at least germany that’s standard so I think it’s just an issue of coding the BCM.


      • in US the rear lights will lit only if your turn Low/Hi beams on or in if Parking light is selected. DRL however will lit if Low/Hi beams are off.


      • I have an Australian car, all I know is that with the headlight stalk in auto mode, the DRLs and the position lights (the ones on the inside of the headlight assembly) come on during normal driving, and then the rear running lights/headlights come on when it gets dark enough and disable the DRL.

        Obviously this gadget keeps on the DRL when the lights are on, I just want to know what is required to make the rear running lights come on automatically with the DRL/position lights so they’re on regardless of the headlights.


  4. I have not installed my DRL yet. Can I return it for the new version? Can it be modified or do I need to order the new version and junk the old one?


  5. Sergey,

    I just installed the DRL harness and it works like a champ!

    I do have a question though. I noticed there are two lead jumpers (not sure if that is the right term), one black and one blue, that can be removed from the harness. After some experimenting, I believe I discovered that removing the blue jumper activates the reduced brightness mode, but I could not figure out the function of the black jumper.

    Blue Jumper In = Normal Brightness
    Blue Jumper Out = Reduced Brightness
    Black Jumper In = ?????
    Black Jumper Out = ?????

    Can you please tell us if the black jumper changes a setting.

    Thank you so much. And thanks again.


  6. I ordered two of these, one for my wife’s RF and one for mine – but of course what my wife wants is to change the color of the LED to match the underglow lights at night. It would have to be at night only, since the DRL need to be white during the day by state law.


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