Removing miata donor parts 2 of 9 Stripping the firewall

Seperate core from mixing unit


Continuing where we left off. The plan is to strip the fire wall to gain full access to the wiring harness in front of the firewall. To do so we need to remove the heater control mixing box that contains the heater core, the AC condensing unit and then the blower fan box. We start with by unclamping the heater core vent clamps, then using a 10 mm socket remove 2 upper nuts and 1 bottom. Pull the box forward. You will need to angle to allow access to remove the plastic side cover located by the core’s supply and return lines, remove the 2 Phillips screws and pull off cover. Now angle, see pic above, the core housing and pull and wiggle to facilitate separation from the core element and put mixing box in the discard pile. Next up we remove the condenser unit. Open hood and at rear firewall we need to disconnect the AC supply and return lines from unit. I should note if your system is charged to appropriately remove the refrigerant. I disconnect the  top line first using a 17mm wrench on the inner but and ¾ on outer and moved out of the way to get access at lower line and using 1” inner and 1 1/8” wrench for outer this line was quickly disconnect. Now from inside the car use 10 mm socket remove condenser housing retaining nuts .Unsnap and remove duct clamp. Pull housing forward and remove the condensation drain hose,

remove moving the condensor unit

Disconnecting refrigerant lines at firewall

see pic, remove unit from car and put in the pile. Finally we remove the blower fan.  Use a 10 mm socket remove 1 upper top bolt and 1 nut located lower right and another nut located lower rear left

removing 10 mm nuts and connectors

. Make sure wiring harness is unplugged (and tagged for future reference) and pull forward and put in the pile. Now we have excellent accessibility to the wiring harness at the fire wall. It is obvious it continues under the carpeting. So I will now remove the carpeting. First I removed the lower drivers and passenger foot well plastic scuff panel by just prying off. Then I removed the plastic and metal door sills, 4 screws each.

remove foot well trim

removing seat should bolts for

I then removed the seat lap belt retainer harness using 17 mm socket for passenger side and oddly enough a 16 mm for the drivers side. Remove the shoulder belt retaining bolts next.

use 10 mm socket to remove clutch rest

Now using a 10 mm socket remove the 2 bolts that secure the clutch rest. Now we are all clear to remove the carpeting. The carpeting is typically held in position by ½”dia. plastic headed one way push on speed nuts. If you want to save the carpet you should remove these by prying off under the head of fastener, see pic,

the correct way to remove trim clips

otherwise you will tear carpeting, I do not plan to reuse the carpeting and must admit to pulling and yanking as my primary method of removal. Start by removing the carpeting by the rear window that covers the fuel tank.

removing carpet over fuel tank

Then I remove the carpeting that is behind the seats. Then after making sure all wires are fed thru the floor carpeting you can simply grab it from the rear and pull back and up and lift to  remove and put in the pile. As you have already observed you have exposed the location of the Power Control Module that hides behind the passenger seat carpeting and  it’s  associative harness. see pic.

PCM and harness along right side

Now this PCM and harness is a keeper we will need for the VortX. So this segment went very quickly taking only about 2 hours to remove all the parts that are in this pile, see pic,

pile of parts for discard or e-bay

none of which are needed for the VortX but many can be listed on e-bay.And a pic of our naked and exposed wireharness at firewall.

stripped firewall and exposed harness

What’s next? Note sure. Need to study a bit. What I absolutely recommend and I consider mandatory is purchasing the  Enthusiast’s Workshop manual for the Mazda MX-5 Miata 1.8L There is also an addition for the 1.6L. I purchased mine at Amazon. The author is Rod Grainger and Pete Shoemark published by Veloce Publishing. For the 1.8L the ISBN # is 978-1-845840-90-7   The UPC# is  6-36847-04090-1.  I will later get the numbers for the 1.6L manual. I will post this info on Reference page when I get a chance. That went pretty easy, So far I have a total of 9 hours in donor.


Removing miata donor parts 1 of 9 or where do I start?

We start by removing the dashboard




Getting started . My first thought is where do I start?

Most build blogs I reviewed do not chronicle the disassembly process in much detail, and why should they as this part of the build is not much fun and is a matter of necessity. But on these pages I hope to post for record the disassembly process I used. I am sure  at the end of this parts harvest I will be more qualified to make recommendation of what or how I would do differently.

At this stage of the build I am still planning of using the factory wiring harness and have decided to start this build by removal of the dash and necessary interior assemblies to allow full access for easier  removal of the harness.

I started by removing the interior dash panel. Refer to this dash removal file.DashRmv_89_93 This is an excellent tutorial with quality photos prepared by Anthony Meeks for Miata owners for a step by step “how to” for dashboard  removal for 1990 to 1993 Miata. My donor Miata is a 1994. I found the procedure to be very similar. On the 1994 there no need to remove the air vent closest to the side widows. There are less screws to remove at glove box. The wiring harness connection will vary somewhat too. But in general just follow the instruction and you will succeed.

The instruction indicate to be very careful when removing the instrument panel cover. This is an understatement. I did break a clip or two during the “wiggling” back and forth process and I did not think I was using much force. The good news is I believe if you plan on using the donor instrument cluster you may need to “trim” the cover to suit the vortX dash shape and the clips are in the area that will need to be trimmed. But at this point of the build I am not sure and recommend extra caution  during this step. Also some notes when you come across the orange/blue connectors, these connector were a bit challenging to get apart.

Blue and orange connectors

you will need to remove the orange one first then the blue one see pic, To do this you need to press hard on the orange clip release  while at same time pulling back. I found where room permits to use a very small screw drive and using like a tongue depressor press down on the flat tap and pull. The blue will release easily after orange is out of the way.

lower column protective boot

Removal of the top half of the lower steering column U joint protective cover see pic is not covered in the dash removal instruction but is easy enough. You will need a 10 mm socket to remove 3 nuts that hold the column in place. You may need to cut or depress some of the firewall sound deadening insulation to get the socket on , but the good news in comes free after the 3 nuts are removed. I retained this part as it may be useful to serve it’s protection duty in the VortX.

Also I labeled all my connectors as I took them apart.. The system I used was to use self stick labels I bought at Wal-mart. They are about 1/2” by 2”. I would wrap an identification letter/numbered tag around the wires of the male connector and an exact same number tag around the female side of the connector. I also used a permanent marker and noted same numbers directly to the connecter halves. I also used a note book and kept record of every Letter/number of every connector I pulled apart. I would also make a note as to the location of the connecter and if I could determine what the connector is used for in a note book. An example of a note would be D19= steering column, igniton switch gear.

The D would symbolize the general area is the dash, steering column give more precise location and ignition switch gear indicates where the connecter was used.

Often I did not have the third level of location. As D18= Dash, near column, main harness connector. This would mean general area of Dash and was a harness connector. It did not terminate at a device but was junction connection.

You can devise any system you want to use. But I think it to be a good idea to use a system that defines the area. For me D= Dash area, E= engine compartment, T= Trunk, PC= power control module, etc This way when harness is removed you can lay it out with reference to the to the general components of the car.

parts removed time 7 hours


Anyway after following all the steps in the dash removal instructions and 7 hours of time  I had the pile of parts removed in this photo.

But we only need the parts in this photo which include the

lower steering column UJ split plastic protection cover.

Steering column with all factory switch gear.

Split plastic switch gear cover and screws. Includes removable 2”x 4” cover.

Solid state instrument panel.

Instrument panel cover

Steering wheel

Gear shift knob.

All hardware for above.

Not pictured but retained for possible use.

Gear shift lever leather boot.

Hazard/pop up light switch.

Center console light.


This ended day one work.  Allow about 7 hours but if you work without interruption you will probably use less time.


What is next?

Here is the picture of inside of car after removal of dash. Here you can see the maze of wires and I must admit this can seem a little intimidating as this stage.

Dash removed and wire and more wires,

For lack of a plan I removed the seats. This was easy enough. Only 4 bolts per seat. My passenger seat required and extra bolt to remove for the shoulder harness. I believe I used a 24 mm socket. I now find the room to work has improved and since we are not going to reassemble our car, I would recommend making this the first step before dash removal as it will make working under the dash more comfortable and takes only 10 minutes.

Next up. As you can see in above picture the  the main wiring harness disappears  behind the heater core housing and blower fan housing. So these are my next targets for removal.



The donor car , and post #1.


transplanted parts will see better days in the VortX.


Pictured is the  1994 First Generation Miata ,Fastcraft motorsport is using for this Build. This car was purchased for a winning bid of $900.00 from the Copart on line auction service. Has 109,269 miles on the clock. The car starts and can be driven slowly. The model year of 1994 was my preferred year. This year and most all 1995 are ideally suited for turbocharging as the compression is lower at 8.8 :1  for these years and the block has blocked off NTP supply and return ports to feed the Turbo charger bearings. Also this year the transmission is more robust and 1994 was the first year I believe to use the larger 7″ ring and pinion. I still have not determined if  this donor has the rather rare Limited slip. Would be a great bonus to find out it is a Torsen LSD but I am not counting on it.Also 1994 and 1995 cars are the last two years before the engine management system has to be ODB 2 compliant. The engine starts easily and sounds good, very little blow by and oil looks good. You always are taking a chance when you buy with out seeing and inspecting in person but I  am pleased with this donor purchase and my winning bid was the max I had set for donor purchase. I wanted to buy the car this way for the experience of using this on line auction. As these salvage cars from Copart are often available for less than $1000.00 they may be a good donor source for our  builders, and at this price for a donor with serviceable engine and drivetrain we are on target to build the affordable performance car for around $15,000.00 target budget for a no frills build..