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 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 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 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 distraction 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 wide range of input voltage.


LED DRL regulator

After experimenting with 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.

This harnesses are available for ordering through my store.

6 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

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