UPDATED 28/12/20: In the USA, it is possible to have the 124 Spider with optional auto-dimming wing mirrors. This isn't an option in the UK, but can it be fitted?

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. In theory, this is a relatively simple retrofit as there's only 3 different elements involved in the entire feature - these are:

  • Auto-dimming rear view mirror
  • Dimming wing-mirror glass
  • Wiring to connect the two systems

However, none of the wiring exists within UK (or possibly European) spec Spiders, and as can be seen below, the feature was only ever designed for LHD cars, so in order to fit this, we're going to have to replicate all of the elements and connections within this system.

The schematic for the system shows that, as in most cars, the rear-view mirror does most of the work and contains the light sensors and electrical control systems of the feature. The wing mirrors merely receive a voltage which alters the colour of the glass.

dimming schematic

The schematic for the system shows that, as in most cars, the rear-view mirror does most of the work and contains the light sensors and electrical control systems of the feature. The wing mirrors merely receive a voltage which alters the colour of the glass. It is possible to fit any Mazda MX-5 or Mazda 6 auto-dimming rear view mirror, although there are better options available, if you can track them down. What is important is the wiring within the mirror connectors - the official wiring is shown below, but we don't need to worry about all of it.

dimming rearview wiring

All we need to make the auto-dimming rear view mirror work is +12V power and a ground wire; to add- in dimming wing mirrors we then need two signal wires which will go from the rear view mirror to the wing mirror(s). Again, note that in the official Mazda implementation, only the LHD (drivers) wing mirror is equiped with auto-dimming. The table above shows that the connectors we need are B and F for power and E and G for connection to the wing mirror. (J is permanent live, but as we're not worried about any memory functions, we don't need that connected)
I've already completed the retrofit of an auto-dimming rear view mirror - I'll post more details of that as I refine the installation; but for now the most important part to noti s the mirror I used - I went for a Gentex series 8  Frameless mirror, which, while now hard to find online, is still available from Amazon - Gentex Series 8 Frameless auto-dimming mirror at Amazon