Good morning all

I am looking at putting in seat warmers in my miata using the EUDM mx5 switches. This will remove the air bag switch, which I would like to keep. Now, I have searched and found a few threads here and there but nothing more putting a cubby hole in the same spot and sticking the OEM switch in the glove box or tucking it away. I would like to not do that. This is what I have, but imagine the blank spot has the seat warmer switch:



So I need to keep the Airbag OFF light, which I will be reusing with the light on the new trim piece since it is already there. My question comes to the wiring. I have found another image from a post about putting a switch in place of the keyswitch:


Obviously I will wire the light into where the above post has the LED to keep the airbag light off in the cluster. My question is, which wire did they use for this? There are 6 wires in the plug for the airbag deactivation switch but only 4 used in the photo. My wiring diagram reading is iffy at best, so I just need clarification.


If I am reading this right, the Black and Red go on one side of my switch and the White wire goes on the other side, so when it is closed, the light goes off and the airbag system is armed. When the switch is open, the Airbag OFF light illuminates and the airbag system is disarmed. Am I correct in this? The picture with the switch from another user does not go into which wires were used, and I am attempting to NOT tear my center console apart unless I am prepared to go from start to finish.

Thanks for the help, I don't want to set the car on fire or flick a switch and have the airbag go off!

 

Yes, you’ve got it mostly covered. Black/red and white should be switched, I believe the contacts are normally open, and closing them is what deactivates the passenger airbag. The “off” LED should be powered off of black/yellow and blue/green. Black/yellow provides +12v and the airbag module grounds blue/green to illuminate the lamp. I’d wager the other 2 wires in the SI-06 connector are probably for panel illumination when the headlights are on.

But just to be explicit and hopefully redundant; that switch only deactivates the passenger airbag. It is used if the passenger is too small of a person and would likely be more harmed than helped in the case of a deployment. It does not disarm the entire system; the driver side airbag cannot be turned off.

 

Thank you for the reply! I know that switch is ONLY for the passenger airbag. I do not carry passengers and even so, I have no kids nor want them in this tin can if so. I will test the wires this weekend with a multimeter, I don't think I have seen the air bag area illuminated at night, or maybe I have not noticed. I do know that all miatas have a "main wiring harness" and the wiring for everything is there, with the factory then putting in the options and blank panels where needed. That may be why the second picture with the switch and light only have 4 wires, for the EUDM may use the missing 2 for night time illumination. Makes sense so that you don't have to fiddle with headlight adjusters with no backlighting.

I am glad to know that the air bag module handles the light illumination, so that is much less wiring I need to do! All the parts I need finally came in... some from the UK, some from Romania, and one "locally" in Colorado.

EDIT: I will post the airbag switch electrical/inside bits this weekend when I get to tear the switch apart without leaving a gaping hole in the center console. Should wrap this thread up, thanks again

 

Thanks for sharing your findings. I'll be making similar modifications shortly and your research re: wiring above is helpful!

 

Thanks bud, much appreciated! On the way home last night I did notice that the "Passenger Airbag" does indeed have a backlight that activates with the driving/headlights. I will get many pictures and wirings set up then post here.

 

Well got it mostly done. I am confident that the wiring is there. I am also putting in seat warmers so its two projects going on at once. I thought I was going to need a SPDT relay to swap the logic but after many hours in MSPaint drawing diagrams and wire colors I noticed a different route that makes more sense and saves me from having to add a relay in the airbag harness. Here is a picture from the back of the airbag switch module. Ignore the toothpicks, I use them to keep the tabs pried apart without marring the housings. Just waiting on some loom to come in to tidy everything up. Hopefully I will get a how-to made before school starts up again.

 

So I got the airbag switch figured out. Again, I am using the EUDM seat heater switch/headlight adjuster in place of the USDM airbag keyed switch. I am sure we all know what it looks like. Ignore the USB-A and USB-C as those aren't part of this story.

So I removed the passenger seat with the (4) 17mm bolts. I then removed the seat belt buckle with the single 14mm bolt. I replaced it with a second driver side buckle so I can use the seatbelt switch that is built into it. Here is a photo, I snipped off half the stock wiring and put a waterproof connector on it for when I need to remove the seat:

Remove the center console, 2 phillips in the storage, 1 phillip on each side of the shifter. There is another under the window switch but after pulling the switch twice I never put it back as it is a PITA to remove. Next I ran the wire from the new connection under the seat area where the flap in the carpet is. I know my carpet is dirty, I have a dog and constantly have the top down. Also any of the grey undercarpet insulation is the DEI stuff from Flyin' Miata, shout out to them for quality products. Run the wire from the flap to the seat bolt area, then from there to the shifter turret area using a trusty coat hanger.

I have it attached to the power window switch area with some electrical tape temporarily while I check if this works. I don't have any pictures from this afternoon as I was spending more time fighting off mosquitos than actually working. Anyways, now is the time to remove the center console surround trim. That is 2 phillips on the bottom, with clips on the side and 2 clips on the top. Gentle pulling or prying with a credit card helps take it off. Unplug the airbag switch wiring, unplug the cigarette lighter wiring.
Here is the back of the airbag keyed module. Ignore the toothpicks, I use those to pry the housing apart without marring it:

You can see they have the wires labeled on the switch. There are also traces that you can see of what wire goes where. Here are the wires after I snipped them, with the corresponding color codes for the Airbag keyed switch (left), Airbag OFF light (center), and the backlight (right).

Hold back the tears when you snip the plug off. You can snip closer to the module if you like, I left a bit of wires for pictures/visual. You can see the plug in the background. Now, I wanted to be able to return to stock if I ever needed to. I do not plan on it, nor will I ever be selling this car, but the option will be there if I need to. I ended up putting a 6 pin connector so I can use the snipped USDM Airbag switch from the car and the EUDM module. You can solder them instead if you like but all the heat shrink I keep is marine grade and the adhesive makes them stiff. Here are the pigtails I now have, the EUDM on the left as a long rectangle, and the USDM on the right as the more square plug.

Now on the back of the EUDM plug, you are going to use 4 of the wires. White/blue stripe, Black/yellow stripe, Red/black stripe, Grey/red stripe. the new passenger seat belt switch will also get plugged into the bridge connector. I labeled these wires Solid black for both. Here is the wiring diagram I made that shows how to wire it together:

So to recap, all 6 wires of the USDM plug are used, and only 4 of the EUDM plug are used. The seatbelt buckle wiring I added later, with yet another plug. Yes, all these plugs are waterproof because its a convertible after all. This is what you should have, and it should indeed look ugly. USDM plug on left, EUDM wired plug in the center with NO seatbelt wiring yet. Ignore the plug on the right as those are my USBs.

Now, plug the USDM into the bridge plug, and plug that into the back of the EUDM module. When you go to install it in the dash, plug in the seat belt buckle plug. There is a notch behind the trim and built into the dash that all this will get stuffed into. Now plug the cigarette lighter in. Go test the seatbelt! Here it is when there is no passenger and the buckle is unplugged. Instead of the AIRBAG OFF light being illuminated, the passenger seatbelt unbuckled light will light up:

Now when you plug it in, the light will go away and the airbag is ARMED:


When the seatbelt is not being used, the buckle circuit is closed. When the seatbelt is put in the receptacle, it opens the circuit. Coincidentally, the airbag module switch works the same way. If the airbag is switched OFF, the circuit is closed. When you turn it on, the circuit is open. The internal SRS Airbag module (the one deeper in the dash) is what controls the signal to turn the light OFF and ON. You CANNOT USE A LED BULB. You have to use a standard incandescent. The module looks for a certain resistance with the bulb and the LED will not supply it unless you add a resistor to it. I do not have the airbag light flickering at all. If you remove the airbag switch module, or use a LED then your airbag light in the instrument cluster will blink and blink and blink... like it has been for me all week until I could finish this up. Hopefully this helps someone. I know I have been searching for this information before tearing into the car with wiring diagrams, but finding a picture of the actual modules from the back was impossible.

Thanks for coming to my ted talk.