This is a story about how to install a kill switch in a Miata, but it’s also something of an ode to two guys named Dave, who factored heavily into this job.
The first is Dave Wheeler, who was the owner of Advanced Autosports, a Spec Miata specialty shop in Beloit, Wisc. Wheeler unfortunately passed away in December 2018, but his shop lives on. Wheeler devised the kill switch kit I used for this story. In fact, I’ve used the same kit a few times. It’s the simplest way to add a kill switch to a Miata, which is what makes it so brilliant.
The other Dave was the founder of a company called Dave’s Custom Boats, DCB for short. In a previous life, I edited a high-performance boating magazine, and one of our jobs was performance testing and inspecting, typically, around 70 high-performance boats per year. We looked where most people never would, under compartments, in the bilge and behind the dash. High-performance boats are hand built, and you never knew what you might find behind a dash. It could either be a rat’s nest of wires or custom rigged perfection, which is what you found on every DCB.
That kind of rigging takes time and effort, and I always admired the workmanship that went into it, and when I do “rigging” work on my racecars, that second Dave is always high on my mind. I doubt he did the wiring work himself, but he hired someone who could do it to his standards, which were high. I wish I had photos to show you. Some of the work was breathtaking, and it’s clear to me that fastidious rigging enhances reliability.
I wouldn’t go so far as to call this kill-switch installation breathtaking. But by taking one’s time, using the Advanced Autosports kit, paying attention to the details, I think it will enhance reliability, something we all value in a racecar.
What I learned from looking at all those boats is that cushion clamps, zip ties and a critical eye are key to building something that looks decent when you’re done. This job takes a couple of hours anyway. Why not make it three hours and turn it into something worth looking at?
And that brings us back to Dave Wheeler and the kill-switch kit that makes the job easier for people who don’t have an ASE certification in automotive electrical systems. It comes with everything needed to install the switch, and it works for all first- and second-generation Miatas. What drew me to it at first was that it didn’t involve cutting or splicing any of the factory harnesses. The instructions that come with the kit list two ways to do the job, the easy way and the way Dave did it. Dave’s way takes more time, but it’s worth the effort in terms of finished appearance and the reliability of the system.
To give a synopsis on how the system works, you’re essentially putting the kill switch between the battery and the starter and connecting the alternator output to the on-off function of the kill switch, which is what shuts the car off when you throw the switch. I’ve never had one fail tech at the required 2,000 rpm.
To get started, remove the positive cable from the battery, cut off the battery terminal and feed it through the hole the floor pan above the rear axle. When you do that, you’ll find it’s taped and loomed to the negative cable to the point where it grounds to a subframe. Remove the tape and the loom and separate the two cables. You’ll also have to move some thinner gauge wiring for the backup lights and one device in the evaporative emission system.
With the positive and negative cables separated, you can remove the positive cable and the reverse-light, and emissions wiring from the power plant frame that connects the transmission to the differential. You will remove all the conduit and tape up to the transmission, then unwrap the wiring for the connectors to the transmission. This lets you separate the battery cable from the trans and evaporative system wiring. Remove the tape and conduit to the point where you can get the battery cable and small wires through the hole in the transmission tunnel where the evaporator case drain is.
Before you do that, take a minute to clean the positive battery cable of all grime and tape goo. I used Acetone, which takes no prisoners. I also wrapped the small wires in new conduit where it passes through the interior.
This is where you learn the hole isn’t big enough to get the reverse light and evap wiring connectors through. You’ll need to enlarge it with a step drill to 1 inch. Put the small wiring connectors through before the battery cable. They won’t fit otherwise. I found out the hard way, of course.
Cut one side the evaporator case drain grommet and reinstall it in the hole around the wires to protect them from the hard edge of the hole in the transmission tunnel. You also might be able to push the connectors through the grommet, then reinstall it in the enlarged hole without having to cut it.
Pull the cable and wiring through and route it along the rocker panel and up to the kill switch, which gets mounted on a plate on the roll cage about where the passenger’s shoulder would be. The theory is that the driver and a corner worker can reach it at that location.
You will have extra positive cable, so cut off the excess and crimp on the copper lug that comes with the kit. That attaches to one side of the kill switch.
The Advanced kit comes with a new positive battery cable that leads down from the other terminal on the kill switch and is routed rearward to the battery in the trunk. It also comes with a length of red wire that goes from that post on the kill switch to the post on the alternator, the one attached with the 12 mm nut.
The existing connector on the post on the alternator, which is a white wire, gets separated from the other alternator connector so you can run it to the battery terminal on the starter.
Separating the alternator wiring is, well, a PITA, but you have to separate them because one will go back to the starter and the other is the multiwire connector that plugs into the alternator. The factory loom is held on with electrical tape but there’s also a black plastic loom that needs to be cut off so the harness can be routed in different directions. It’s difficult, so take extra care not to damage the insulation on the wires. I used scissors rather than an open blade.
You’ll need to cut off the eyelet that connected the white wire to the alternator and crimp or solder on the supplied eyelet that fits over the positive post on the starter.
That describes the essence of the job, but for the gritty details, refer to the photos and captions.