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.
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.
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.
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
Insert my harness and put everything back.
Now DRL will stay on with reduced brightness when headlights are on.
This harnesses are available for ordering through my store.