You might be wondering why this item is in the 'Suspension' category... When you lower your ND the sensor in the rear which adjusts your headlights down to compensate for weight in the boot gets really confused and over adjusts leaving your headlights pointing down at the ground (which is not good) This adjustable rod replaces the stock one and fixes this issue.
In more detail basically the sensor is there to ensure that the headlights don't point to the sky when you have a load in the trunk. Since it only measures the rear ride height, it assumes that a lower rear ride height equates to a low tail and a high nose. It compensates by aiming the headlights lower. It can't tell if you've lowered the front of the car as well, it's working on the assumption that it knows the stock front ride height.
Suits all lowered MX5 ND 2015> models (One required per car)