I have recently fitted power locks (and connected them to the remote-controlled alarm) on my1995, mx-5, 1.8i, "california". Ben Lawrence's article about this subject on miata.net was really invaluable, especially the pics - many thanks Ben. Definitely read his article first.
I thought it would be useful for those of us in the UK if I listed the supplier of the door lock motors etc and also highlighted how I got around one or two hassles en-route.
The door-lock motors (gun-type) can be obtained from Maplin Electronics (there are lots of stores in the UK - call 01702 554000 for the nearest one). Their part number is YD79L (2 wire version) and the motors sell for £5.99 inc VAT each. They come with the bits that Ben describes ie: fixings, bracket and connecting rod, although there are no bolts included to actually mount the motor to the bracket. I didn't realise this until I got home from the store (30 mile round-trip!!) so I used No.8 X 1 inch screws which I happened to have although something like an M4 X 20 bolt and nut would be better from an engineering viewpoint. I promise to change them some day. While in Maplins, you can also get a packet of tie-wraps, fuses, wire and crimp connectors etc.
The fixing brackets seem to be a little shorter than the ones shown in Ben's article and only just fit across the top of the aperture in the door - but they do the job. The connecting rods were bent into the "lazy Z" that Ben describes and basically the installation looks pretty identical to his photos.
The car came with a remote controlled alarm which monitors the doors etc and also uses ultrasonic detection (when the roof's up!). There is also the facility to operate central locking motors. It's a "Cobra" alarm which is a well-known make in the UK. The car came with only the operating instructions for the alarm and not the installation instructions, but Cobra were very obliging and a phone call to them resulted in a faxed copy. Before starting any installation work, I tested the door-lock motors and the alarm's ability to operate them with a temporary lash up just to check they actually moved in and out - they did! I also ascertained at this juncture which polarity made them move in and which out. Basically, applying 12v to one lead and ground to the other causes the door-lock motors to move out and reversing the wires causes them to move in.
Getting the door panels off was surprisingly easy - I had to remove the grip used to close the door (2 large screws) plus the back plate for the handle mechanism (1 small screw) and one largish screw located behind a cosmetic cap at the rear of the door pocket. The back plate comes away easily (after removing the screw) with just a little bit of jiggling to get it around the handle mechanism. The window handle has a U shaped clip behind it which I extracted with a small screwdriver and a bit of gentle levering - the handle then simply pulls off.
There are a number of pop-studs situated around the perimeter of the door which simply just pull away with a firm tug. There is also a locating stud at the top of the panel, and once the other pop-studs are released, the door panel can be lifted upwards and away.
Inside the door you will now discover the plastic sheet attached with "tar" to which Ben Lawrence refers. At this stage, I went a different route to Ben as he advocates removing the plastic sheet. Since it already had a slit in it for the existing mechanism, and that tar looked really sticky and horrible, I decided to cut an additional slit in the plastic with a craft knife where it covered the aperture I was trying to get to. I reasoned that if it had one slit already, it wasn't intended to be watertight.
In order to mount the bracket, I drilled a 2.5mm hole at either side of the aperture to take theself-tapping screws that come with the kit. Again, M4 bolts would probably be better, but I didn't have any and I was eager to finish the job! Don't overtighten these screws or they will just turn and turn! I actually put a small dab of locking compound on all the mounting screws for peace of mind.
Bending the connecting rods by hand into the "lazy Z" was simple enough. Getting exactly the right angle takes a little trial and error but it's not that difficult. The connector (supplied) which holds the door-lock push rod to the door-lock motor connecting rod works really effectively and is easy to fit with the 3 small bolts supplied.
So far, so good - all the mechanics mounted and a simple wiring job to finish. Each door-lock motor needs 2 wires to connect at one end to the 2 short wire-tails that come with the motor and at the other to the alarm under the hood (bonnet in UK-speak). I cut 2 long lengths of suitable wire in different colours and twisted them together to make them look neat. A quick way of doing this is to clamp one end of the two wires in the chuck of an electric drill and get someone to hold the other ends at their full length. By running the drill slowly, the wires will be twisted together very rapidly and look very professional. Don't overdo the twisting or you'll knit a sweater!
I used some insulated crimp connectors to attach the wires to the door-lock motors and thentried to feed the wires through the rubber tubing betwwen the door and the body of the car that carries the door loudspeaker wires. This was the most difficult part of the whole job. It was instantly clear that the two soft wires would never push up this crinkly, corrogated and bent rubber tube. Simple I thought - I'll use some stiff copper wire from a mains cable (earth lead), wrap it around the end of the motor cables, feed that through the tube and pull the cables through. It eventually worked but even on the second door, having had practice on the first, it was no easy task - you need a finger with a joint every 3 mm!! I temporarily pulled the tubing out of its end location on the car body to assist the process and unscrewed the loudspeaker to enable me to get my hand inside.
On the (UK) passenger side I ran the wires through a grommet in the firewall that is located just below the windscreen washer bottle. If you remove the glove-box lid by undoing the 2 screws at either end of the bracket to which it is connected it gives easier access. Also there is a large rubber conduit through which the ventilation air travels from the fan to the vents. This can be undone at the fan end very simply by pulling out a single pop-stud. This gives masses of room for crawling about with your head under the dash board. Don't forget to put it back afterwards (the conduit - not your head!).
On the (UK) driver's side I ran the cable across the car from right to left behind the centre console and above all the pedals. Use generous quantities of tie-wraps to ensure the cables are safely out of the way. I then joined the right side cable to the left behind the firewall and ran the rest of the left-side cable through the firewall grommet. Make sure you use the same colours on the respective door-lock terminals or else you'll have a car where one door is always locked and one always open and pressing the alarm 'on' button will reverse the mode!
I followed the alarm instructions and connected the door lock cable to the correct wires and voila - it worked. Before reinstalling the door panels, I stuck the slit in the plastic sheet together with a length of 'sellotape' (scotch tape in the US). Locate the top stud first on the panel and then push the other ones home firmly. Incidentally, while the panel was off, I took the opportunity to grease the window runners. The windows go up and down like silk now.
Screw the fittings back on and jiggle the door opener back plate into position. If you install the clip back on to the window winder before refitting it, the winder will simply push back on to the spline and lock into position. Having done this on one side, I then realised I had missed off the plastic washer that goes behind the winder and so had to remove the winder again - swear word!
It was very satisfying to complete this job which in total took about 4 hours. You could do it in less time but it was a beautiful sunny afternoon and I wasn't in a hurry. I convinced the kids with a bribe of an ice-cream to pick up the dozens of tie-wraps and rubbish I had thrown around and sat back to play with the mechanism for about an hour. If you wanted, one could also fit a DPDT switch inside the car to operate the door-locks for use as a safety feature. Not much use with the top down though!
I reckon this was tremendous value for money at less than £20 all in. The added convenience plus the fact the keys won't mark the paintwork anymore and knowing that the satisfying 'clunk' you now hear every time you switch on the alarm is your own handiwork makes the effort all worthwhile. I hope this article helps you with your installation.