Miata Kill Switch

By Keith Tanner

(Additions from Stu Jessop and Jerry Fuller)


This is an easy enough installation. I'll try to make it nice and simple. The whole thing took me about 1.5 hours (a guess), but if I did it again, it would probably only take about 30 min.

First, pick where you want the switch. This may sound obvious,but you'll need one that fits in the place you have picked out. Mine is in the same place as the trunk release would be on a later car-beside thefuel filler release. This is lockable, so it's a bit more secure, and also out of sight. You could also put it in the glovebox, but that's a bit inconvinient, and the switch is only effective if you use it.

Then, find a switch. I got mine at Radio Shack, but to each their own. You'll also need some wire (black looks "factory"). That was easy, right?

I installed the switch in the console next. This was the longest part of the job. Take off the armrest (screws are at the forward edge, under the glovebox, and in the storage bin. You'll also have to remove the shift knob. It unscrews.) You may also have to take off the cover for the part of the dash containing the ventilation controls etc. To do this, remove the screws at the bottom edge, and pull out the vents at the top. They're stiff, but just pull straight out with a pair of pliers. There are two more screws hidden in behind there.

After you've drilled the hole and installed your switch in the console, feed the wire through underneath the radio (there's a handy hole there) and into the footwell. There's lots of room (unless you have the CD player, perhaps).

Now get into the footwell of your Miata. There's a white plastic switch assembly that the clutch hits when it goes to the floor. There are two wires coming out of this, attached together with black plastic. This wire goes into a white plastic connector after about 6 inches (15 cm.). Disconnect this (it snaps apart if you push the correct latch) to give yourself some more working room.

If you can find another connector like this, you're laughing. According to my dealer, the only source you'd be a donor (read "wrecked") car, and that was too depressing a thought for me. Otherwise, cut one of the two wires. Now your car won't start at all, so don't decide to go driving here. This is where the wires to the switch attach. There are all sorts of electrical connectors on the market - soldering is not necessary. Now try it. If it works, put it back together. If not, checkthat your connections to the switch are okay.

One final thing to make the work invisible- you should be able to move the part of the wire with your new connection up on top of the fuse box (I THINK it's the fuse box) so you can't see it. Make sure everything's secure and won't vibrate or pull loose.

There you go. I hope this was clear enough for everyone who asked. Let me know if you have any further questions, I'll be glad to help out. Also, if anyone does perform this operation, let me know. It's nice to know if I helped at all.

Keith Tanner and Baby

ADDENDUM: 18 months later, the only change I might make would be to use the cigarette lighter as the switch. Pushed in means on, pulled out means off. For maximum security, take it right out. You would lose power to the lighter in the easiest installation, though. Keeping it live should be possible, though.

From Stu Jessop on cigarette lighters:

What I did is this: Cut one wire of the pair that goes to the clutch disconnect switch. Solder two wires to the ends and run them to the lighter plug. Solder these two wires to the two wires for the lighter plug.

Theoretically, when the lighter is fully inserted, it completes the circuit, thus the car will start. However, it did not work. I don't really understand why, the lighter assembly makes a good circuit with the lighter inserted, as I said, about 10 ohms resistance. But the only way I could get it to work was to wrap the inner part of the lighter plug with thin copper wire and then tin it with solder. Now it works exactly as I had planned. In fact, this is even better than I had thought. Now if somebody figures out what I've done, they won't be able to use a stock lighter from another car to defeat it. (of course they could just cut the wires, but how paranoid can I get?)

So, that's the way it works.

From Jerry Fuller :

The "My Pain, Your Gain" Miata Kill Switch Story


Yes, after a long day proving to my 34 year old body that it can still bend like a 3 year old (at least until tomorrow when the stiffness sets in), I succeeded in wiring in a kill switch using lighter as the switch. 

I wanted to share the story because there were a few learnings along the way, so hopefully you won't make the same mistakes.

Executive summary:




Why I felt I needed a Kill Switch:

I park in the river valley, ten minutes from work. There's not many homes near by, only abandon cars of cheap parkers like myself. I have known two friends who have had their car stolen from the valley. The cops told one of them to pull the ignition fuse each morning to prevent another theft. Yeah, that'd be handy <g>...

 I decided to follow in Keith Tanner's footsteps and wire in a kill switch. Keith chose to locate a switch in the lockable console, but I wanted it a little handier. The lighter is only 3 inches from the ignition - can't get much handier than that. Now to start the car you have to know you need to push in the lighter.

 I don't smoke, nor do I use a radar detector, so I didn't have much need for the lighter. If I decide I want to plug in an accessory it's pretty easy to pick up an accessory plug at "Canajun Tire' and wire it up.

 Here's the 7 easy steps to wire in the lighter as a kill switch.

 Step One:

Buy small package of 10 guage wire. You'll need about 4 feet but will undoubtably end up buying about 25 feet.

Buy small package of 18 guage wire. Just about any wire will do, but this lighter guage stuff is easier to work with. You only need about 3 feet. Even half a cord of lamp cord will do.

Buy package of 10-12 guage butt connectors. The type you crimp on to connect one bare wire end to another.

Buy 12 volt, single pole relay, 30 amp or so. BIG HINT: Don't buy a 70 amp relay - it won't work... trust me :-) I found one at Radio Shack for $10.

Buy package of push together 1/4" connectors (plug in type - type you can insert and detach). At least that's what my relay needed. In other words, buy something to connect wires to your relay.

 Step Two:

 Prepare the car and your back. Remove driver seat, plastic chunk under steering column (two phillips screws then pull it downward from the screw end - gently), and touch your toes 30 times (ok, its optional, but all the pros do it). There's not much room to work under here. My arms are still sore. Remove ground from battery... just to be safe.

 Step Three:

 Identify the wires running through the clutch switch. The ignition circuit requires both the key to be on 'start', and the clutch to be depressed (sorry, I have a five speed; if you have an automatic this won't apply). See before and after pics below. Careful, there's two switches on your clutch. One for the criuse control which is there whether or not you have cruise control. The one you want is near the floor. The clutch needs to be pushed down to the floor to empower the switch. There's two green wires wrapped together from the switch which route above the fuse box and to a harness plug. You can disconnect the plug to give you a bit more room to work. The wires are sort of clipped up above the fuse box, but you can feel the clip, and unclip it to give you more room to work. You will know you have the right wires by disconnecting the harness plug and trying to start the car - remember to connect battery ground if you choose to do this test.

 Step Four:

 Cut into ONE of the wires and use butt connectors to crimp on two two foot pieces of 10 guage wire - one to each end of cut. Note, car won't start right now, so don't do this right before you have to take kids to swimming lessons...

 Step Five:

 Connect 10 guage wires to Relay. The relay will identify four connectors. Two will show they are for a open/close contact. This is the one you want. The contacts are open until current is passed across the other two connectors. Now before you crimp on connectors to connect the heavy wires to the relay, you need to subdivide off some ignition circuit's power to go to one of the other two connectors. You use the ignition circuit's power to _also_ go through your switch (lighter). You could solder a wire across the two connectors, or do as I did and using a short two inch piece of wire jumper between them. (see diagram)

 Step Six:

 Connect Lighter to relay. Pull out your lighter. If you pull it out sort of at an angle it will pull out the socket and all. Gently now. I don't want to be held responsible for broken dash. Or, reach around the back and push the socket out. There's two wires connected to it: power and ground. The ground is connected to the casing of the lighter socket, and the power is connected to the screw in the centre of the casing. There is a black plastic harness holding both wires so they plug into the lighter as one. Now however you want to do it, the goal is to disconnect the 12 volt source, and run a light guage wire from the relay to the positive (power) connector on the lighter, and have the power pass through the lighter and out the ground. I cut into the ground. I crimped on a 1/4" plug in connector, and folded the wiring plug and power wire back,and taped them up. Now I had the ground connected to the lighter, and a new lead from the relay to the lighter's power lead (the centre one) (Yes! We do spell centre that way in Canada).

 Step 7:

 Find somewhere under your dash to mount your relay. On my car there was a conventiently located bracket sitting there unused. The relay will have a hole for mounting it, so it should be pretty easy. Now tape up your work to secure it all, and help it blend into the naturally occurring darkness under the dash. Push the clutch switch wiring back up on top of the fuse box. Hopefully your splice will be well hidden by the fusebox. Reassemble car; seat and underdash piece of shrouding.

Oh yeah! Test it before putting it all back. I figure you'll do that, but I figured I'd mention it. You'll have to make sure you reconnect your battery, or else you're sure to be dissapointed :-)

If you try to run the clutch switch wires directly to the lighter (i.e. no relay) you will find it won't work. There's too much resistance in the lighter. That's why the relay is used. If you really didn't want to use the relay you could solder some wire into the lighter to bypass the lighter coil, but one such previous attempt resulted in the wire coming loose after it got 'heated' up repeatedly.

The first relay I bought from an electronics specialty house was a 70 amp. It wouldn't work, so make sure you get a lower rated relay.

So, now I can sit at my desk at work, looking down upon my car about 400 yards (and five minutes if you run) away, and feel secure.... and hope I don't run across a thief who smokes and decides to light up before jammin my ignition switch :-)

Good luck. Feel free to write if you have any questions...

Jerry Fuller
'90 Classic Red
Team 'too many to mention'
Wild Rose Chapter of MCA