I have collected information and added my own input on this conversion.


**While doing the NA to NB interior conversion, you may wish to switch the carpet to the NB material, as it is made of much nicer material and in my opinion much more comfortable.**

There are a few issues that need to be dealt with when doing the NB interior conversion. In this section, I will explain the wiring portion of the swap.
The NB dash will bolt up perfectly to an NA Miata; however, the wiring harnesses are different. You need to remove the NB Harness from the dash, and replace with your NA harness. For the most part, things reach where they need to. Your combination switch, consisting of the pop up light switch and the hazard, will not fit without much modification to the NB dash. You can wire the NA hazard switch to the NB switch. This needs to be wired as follows:

Hi all, I just wanted to post this up for anyone who does a search for a hazard button retro fit: NA Miata NB hazard button.
Here are excellent instructions for this by jcc011185 for a NA to an NB (2001 and up).
I have a 1997 Miata with a 1999 dash put in. The wiring used on the 1999 and 2000 hazard button is a bit different than that used on a newer model NB (2001 and up). The wiring is as follows:

NA 1997 Harness to NB Pigtail 1999
Orange to Orange
Black to Brown/White
Red to Grey/Red
Red/Black to Red/Black

the only difference is the Black NA wire to the Brown/White NB (1999-2000) wire, rather than the black NB wire (2001 - ?)

The NB gauge cluster will not be plug and play to your NA harness, for a number of reasons. Fortunately your NA cluster will fit in the NB dash with little modification. All that is necessary is a little trimming of the dash where the speedometer cable inlet is located.

After you get through that, the dash should bolt right up to your NA Miata. You may have an issue with the knee panel under the steering column. Mine kept on popping out. If you are swapping the steering wheel, I recommend swapping the clamshell as well.

Swapping the steering wheel is fairly simple. The splines match up, but the NA clockspring tabs do not. There are a few ways to get around this. You can drill or cut holes in the back of the NB steering wheel to match the NA wheel cuts. You could, instead, just move the clockspring to the NB slots. The drawback of this option is simply when you are turning, and are done; your turn indicator will not automatically shut off every time. Or you can swap the NA clockspring and ignition cylinder with an NB. This requires a bit more wiring work and modification to fit.

Depending on whether or not the NB dash you purchased came with a passenger airbag or not, you will need at least a cover. Covers can be purchase for less than 50$ from businesses that sell Spec Miata parts. I’d recommend going through Panic Motorsports. If you already have an airbag, in the interest of weight savings, you can remove the actual airbag from the cover and just place the cover over the airbag slot.

The center console bolts up with no modification at all.

To make the HVAC controls work; you will need the NB HVAC controls. The NA controls won’t fit. The problem with this is the differences between the connectors. Fortunately the hard work has been done for you; it’s easy to construct an intermediary harness, by using the diagram provided to you thanks to Miata.net.

The cables/sliders fit without modification.

Begin by cutting out all the wires from the NA controls. Then acquire a pigtail for the NB controls. Use this diagram to connect the two to construct a removable, plug and play intermediary harness.
Here's the wiring matrix:

A refers to the plug on the car-side of the harness.
B refers to the NB pigtail.

A-P1 -- AC3 & B-P4 (fan speed 1)
A-P2 -- B-P5 (fan speed 2)
A-P3 -- AC1
A-P4 -- diode* (inline) to AC2
A-P5 -- B-P3

A-S1 -- B-S2 (fan speed 3)
A-S2 -- B-S3 (fan speed 4)
A-S3 -- B-S1 (ground)

L1 -- B-P1
L2 -- B-P2

* Use one of the two diodes in the NA A/C switch...either hack your original or one from a junk yard.

See attached picture for the 3 types of plugs you will be using.
Refer to the photo via this link to Miata.net


The finished harness should look something like this:


Once you have completed that, you are done with the dash and center console.

The NB seats are bolt ons, and they are a few pounds lighter than the NA seats.

The NB door panels require the most work out of any other part of the NB interior conversion. While the NB door retains the same shape, the mounting points for the NB doors share nothing in common with the NA mounting points. The 01+ door panels are also different and harder to fit than the 99-00 door panels, so I’d recommend going with the 99-00 panels. The write up for the NB door panel installation is located in the “Garage" section of miata.net. The link is here:

http://www.miata.net/garage/door_panel/index.html

If there is anything that you need help with, please feel free to send me an email, my email is
citrguitarist@gmail.com
Thanks for reading!

I want to thank Miata.net and it’s users/admins for their experience, and being kind enough to share it with the less experienced.
I also want to thank everybody at Panic Motorsports for allowing this project to go through. The NB interior is truly a worthwhile upgrade. Visit Panic Motorsports at Panicmotorsports.com.

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Thread moved to correct section.

Great work btw!