[brosmar1]

So, with all the recent talk about theft, my goal was to create an anti-theft system that will retain my warranty, allow me to easily return the car to stock if needed, and deter theft in some way. This does not involve any cutting or splicing into factory wires, the most destruction you will have to do it take a dremel to two small plastic parts. I do not lose any functionality that came with the car from the factory. And it does indeed immobilize the car when activated. Buckle up, this will be a bit of a read.

Before going any further, I highly recommend taking a look at this thread as you may not understand the switching device without it. One of my exhaust actuators stopped working (2nd one in 4 years, go figure) so I removed both and have had this switch sitting under my dash doing nothing. It got me thinking how I can use it for something else the car desperately needs, such as a better anti-theft system. If I can control the exhaust fuse from the cabin, why not the fuel or spark fuse too?

So I set out to test all the fuses that may work to kill the car when pulled. There are 7 I came up with as viable candidates:

F13 - Starter
F41 - Malfunction indicator lamp/ignition
F50 - Fuel system control module/ignition
F57 - Engine control module/ignition
F58 - Transmission control module/ignition
F66 - Engine control module 1
F67 - Engine control module 2

Seems simple, pull any of those fuses and the car wont turn over, right? That's what I thought too..

From my testing on a (basically stock) 21 2SS, there are only two fuses on that list that actually kill the car. Those being F13 and F67. Every other fuse allows the car to start (and drive, for that matter) when pulled, although they will all throw a permanent code that will need to be manually cleared when triggered. So lets take a look at F13 and F67 and the behavior when each are pulled.

F13: Starter will not crank when key is in vehicle and ignition button is pressed. Electronics will still turn on, but not much else happens.

F67: When key is in vehicle, the starter will engage and spin the engine but no matter how long it cranks it will not turn over. Electronics work as normal, check engine light present. Scanning the codes gives a permanent P1682.

Both seem like fine options, but I chose to go with F67 simply because it is a Micro2 fuse and that is what my harness is suited for. So lets explore a little more into what happens with F67 on a switch. To note, the fuse is specified as 25A and I used 14g wire, which ranges in ampacity 15-25A depending on the grade. I have not encountered any issues in two days of driving.

As stated above, when the fuse is pulled and engine attempted to start, it will throw permanent P1682 code. This is actually my favorite part about this mod. The fact that I have a reliable log to see if anyone tried to start my engine when the kill switch was engaged (if broken glass or destroyed trim panels don't already give it away). Works on thieves as well as joyriding children!

As soon as the switch is disengaged (or engaged, depending on how you want to look at it) the car can start up and drive as normal. I would not recommend flipping the switch while the engine is running. It made a very ugly sound but did not throw any codes or cause any other apparent damage.

Of course there are weaknesses with this method.

The most obvious is the wire running from the fuse box through the firewall. Once a problem is realized, a savvy thief could open the hood and cut and jump the wires and be right on their way. I am sure you could tap into the wires coming out of the bottom of the fuse box and have a much harder to trace system, but one of my main goals was to not cut into any factory harnesses.

The second greatest weakness is the switch itself. With the parts I linked in the other thread, you are stuck with this heavy duty 50A switch staring back at you when you peek under the dash. A relay and a more inconspicuous microswitch would allow you to hide it much better, but will complicate the wiring and may open up other weak points. I will look for a better hiding place, but I cant share all my secrets on here

At the end of the day, if my car is a target and this adds a couple extra seconds to the process, they may very well decide it is not worth their trouble and move onto the next score. I hope those that read this in its entirety consider this mod, as it is fairly easy to install and can be returned to factory state in just a couple minutes. If anyone has any questions or suggestions please leave a comment. And if anyone has any qualms about sharing too much information to would-be thieves, I say let them read this and know we will no longer allow them to make a quick buck off our hard earned babies.

[brosmar1]

This seemed like the most relevant sub to post this under, please move if it fits better elsewhere.

[Keko]

Thanks for sharing. Doing something like this has been on my mind for obvious reasons.

[DamonZ28]

The Mobilistics anti-theft device is even easier. Simply replace the starter relay, and use the remote before you are able to start the car. No wiring, no switch.

[brosmar1]

Originally Posted by DamonZ28

The Mobilistics anti-theft device is even easier. Simply replace the starter relay, and use the remote before you are able to start the car. No wiring, no switch.

I agree, but I had all the wiring in place already and wanted to do some experimenting. Layers of security to fall back on is always better!