In the USA, it is possible to have the Fiat 124 Spider with an option of auto-dimming wing mirrors. These mirrors change their reflectivity based on ambient lighting conditions (e.g. glare from other vehicle lights during nightime driving).

The system works by taking a feed from the interior rear-view mirror (which contains the ambient light sensor) and then instructs the mirrors to change their reflectivity accordingly.

This feature is something that I've heard requested numerous times, especially as you sit so low in the 124 Spider. Unfortunately it seems that this is quite an awkward feature to retrofit.

The items required for this system to function include (this list may not be exhaustive)

Auto-dimming rear view mirror
Auto-dimming rear view mirror wiring loom
Auto-dimming wing mirror body
Auto-dimming wing mirror glass
Auto-dimming wing mirror wiring loom
Car body -> door wiring loom including auto-dimming wires

Unfortunately, it seems the auto-dimming option isn't available on any UK-spec cars as I'm unable to find any Mazda parts which have the necessary wiring; let alone the in-vehicle wiring we'd need (which definitely doesn't exist in UK-spec cars). So for now; this project is a no-go