Keyless Entry Upgrade for 01/02 MK2.5 01/02/03

WARNING, due to the unatural angles you will require to distort yourself into to complete this job, you may need to seek the services of a Chiropractor afterwards. !

Keyless entry on the MX5 MK2.5 is standard on the sport and some special edition models, the practicalities are obvious for this facility but I also wanted to stop the door getting scratched by the bunch of keys. Having decided a mod was in order I set about the task of finding a suitable kit at a reasonable price, little did I know how hard this would be. 

My first port of call was the main dealer, after talking to several I came to the conclusion that the OEM parts (about £200) were not suitable for retro fitting. In fact if you have this mod done at the dealer then it's quite likely they will sub the work out to an Auto Electrician to fit an aftermarket unit anyway. One dealer quoted me £310 !

Installation is made a little easier as all post 01 MX5's have actuator motors in both doors. You will need to check this before purchasing your keyless entry unit. You can verify this easily, unlock the doors and then lock them via the passenger side, if the drivers door locks then you have actuators in both doors and you only need the Keyless Entry Module to make this work.

So, having decided a dealer fit kit was a little pricey, I chose a kit being sold by "MX5 parts" for a very reasonable £62 which included two remotes. This kit however is not supplied with bespoke connection info for the MX5 let alone a MK2.5 with a somewhat more complex central locking system, it's down to you to find that out.

After several weeks of scanning the internet for info, I found that there is loads of information and systems out there for the MK1 but very little for the MK2.5. I have also been unable to locate a set of wiring diagrams or workshop manual for this model, this would have helped enormously. I was hopeful that our friends at Miata Net in the USA would be able to help, but it became quickly apparent that the USA spec car is wired differently, I put this down to amongst other things the UK Cat 2 immobiliser and alarm system. There is a good article in the Miata garage for a 99 model, however the connection information is not the same for either later UK or USA cars.

The solution was finally worked out by Max from Maximum Impact a professional Alarm and Audio installation company in Leeds, after sending him the pin out drawing below of the DLM (door lock module). He suggested that a 1K resistor was needed in the lock circuit, he also suggested that the lock signal be via a relay. Apparently the UK MX5 uses a similar system to the Ford Probe. A massive thanks goes to Max for his help and I can definitely recommend him as somebody who knows his stuff, so if you need the services of an alarm installer in the Leeds area give him a call on 0113 244 1448. 
Another good reference site for 12V and relay info is Here.

Kit Details

The  MX5 Parts kit is a 3 channel system, the second and third channels can be used to operate other facilities e.g. remote boot release.
Note, the picture on the MX5 Parts web site is of the single channel system not the 3 channel. I was a little disappointed with this as the single channel fobs look much slimmer.
A different unit could be used, the wiring diagram would be the same if it has -ve outputs. A single channel system would suffice if only door locking/unlocking was needed.

The KEU (keyless entry unit) also has several other outputs including interior light activation and horn beep, these may added in the future. Lock and Unlock output triggers are  -ve 300ma. The quality of the key fobs is not great but the unit seems to be robust enough.

Other facilities available are Autolock which is selected via the dipswitch on the KEU, starter interrupt and L.E.D activation warning. The starter interrupt is not required on the 02 as it already has an immobiliser, I also didn't bother with the L.E.D as I prefer to keep the installation as invisible as possible, besides which there is already a dashboard warning light. The KEU also has supplementary 12V and ground outputs which could be used for window closure e.t.c. The unit has an option for an extended pulse trigger, this is not required for the MX5.
The standard alarm system will continue to operate in the normal way, it will be activated when you lock the doors.

I chose to attach the KEU to the panel below the steering column, although it could be mounted anywhere behind the dashboard. The panel is removed by undoing the two screws on the lower edge, you will then be able to slide the panel downwards. 
There is enough room behind this panel to mount the KEU directly to it, you need to site it as close to the bottom edge as possible to clear the large connector going to the steering wheel. 
Mazda have kindly supplied a couple of standoffs that can be used to mount the unit, this saves any unsightly screw heads being visible on the outside. Cut two short lengths of strapping and mount the unit as shown, use the captive nuts to secure to the lugs on the KEU. Use care when screwing the straps to the standoffs as screws that are too long will  breakthrough the cover. The relay was attached to another of the standoffs on the cover.

Once you have securely mounted the unit and the relay, continue to wire them up using the diagram below. You should be left with 4 wires leading away from the panel. 
Also seen in this picture is the aerial, I simply attached this to the back of the cover with a piece of tape. For the sake of neatness I chose to remove the unused wires from the large connector on the KEU, this is easily done by using a sharp tool to push down the sprung part of each socket seen here on the right, the wires can then be pulled from the connector.