Go directly to: Adding the interior switch
Adding the exterior switch
In the U.S., with the Advanced Keyless Entry (AKE) option, in addition to the interior trunk release switch (near the hood release lever), our 124 Spiders also gain another switch on the underside overhang of the trunk lid itself in-between the pair of license plate lamps and, if you have the Infotainment system, to the right of the ParkView reverse camera. Mazda has thus far decided to exclude the camera in the MX-5, and in some markets (like Canada*), that exterior trunk release switch, leaving only the interior switch to release the trunk lid.
Limited feedback I’ve received indicates that Fiat includes this switch with the AKE option across all markets, but just in case Fiat has also chosen to exclude that switch in a particular market, I’m bringing up a solution that Sergey (ssh16) has come up with as a nice alternative, and that JumperThumper has verified in his Canadian MX-5, which involves “piggybacking” the exterior switch (don’t know the Fiat part number, but the Mazda part number is N243-56-8D0) with the interior switch, as the wiring back to the Body Control Module (BCM, inconveniently located behind the left kick panel in close proximity to the interior fuse panel) should already be in place.
The piggybacked switch will actually be more convenient than the intended application, as you won’t need to have the key on your person to activate the exterior switch. It will work whenever the interior switch is allowed to work ⇒ whenever the vehicle is unlocked. When both doors of the vehicle are locked, both trunk release switches will be deactivated.
So just how did he accomplish this? He made a jumper wire (≈6″ long) and with quick-splice wire connectors, he connected together:
- the yellow wire that is plugged into terminal “2S” on the largest BCM connector (#2 of 3) that connects to the exterior switch
- the brown/green wire connected to the interior switch that plugs into “3U” of the other (hidden) BCM connector (#3 of 3)
There are links to wiring diagrams and illustrations in the referenced thread.
* According to Gordon, the reason 2016 & 2017 Canadian MX-5 vehicles didn’t get the AKE option, nor the exterior trunk release switch:
Transport Canada would not allow it, because the rear trunk switch was too low to be handicap accessible per their guidelines. It took them three years to acknowledge that no handicapped person was putting a wheelchair in the trunk of a Miata and that their refusal was asinine, and they finally relented, allowing the system on the 2018 models in Canada.
Adding the interior switch
For those that have wiring leading to a dummy insert (as pictured below) rather than an actual interior switch (Europe and Australia market?), a few readers have already discovered that purchasing and installing an interior switch (Mazda part number GJR9-66-630A) and plugging in the harness (only present in LHD cars) will not, by itself, enable it’s function.
However, I’m happy to report that collincn has verified that Sergey’s solution works inversely ⇒ piggybacking the added interior switch to the exterior switch (as illustrated above) will enable the added interior switch to function, although only if the requirements allowing the exterior switch to function are met (i.e. with AKE, you’ll need the key on your person, as is required with the exterior switch).
Keith (@jamiesk) has taken this procedure a little further, since his RHD (UK) Miata has a blank plate in place of the “boot” release switch, but located on the other side of the vehicle, where access to the BCM is much more difficult. Note that, unlike LHD, it is unclear if there will be a wiring harness to plug into the added switch, or not. You can read his write-up and see his additional photos here.
I found the yellow wire from the external boot switch in the left-side door sill harness (RHD passenger side). There are several yellow wires, but the others are larger wires and twisted together. The yellow wire you need is the small one. I cut it and spliced in a small extension, soldering on the new cable. I took a cable around the back of the cockpit to the switch.
The cable route was alongside the existing wiring to the rear, behind the passenger side soft carpet, over the transmission tunnel by pulling up the centre console, behind the drivers side seat carpet, follow the existing loom forwards and up behind the dash, through the “rear to front” cable connections white box and then onto the switch.
I then cut the brown/green with enough length to solder the new wire to.
[The two wires will be connected to the two outer pins of the switch module (the two inner pins are for illuminating the trunk icon on the switch).]
I now have an internal switch that works in parallel with the rear external switch.