A "Remote Engine Disconnect" is a common feature on all but the most basic vehicle alarms this days. However they are not all created equal, and many work in very different ways. The ideal implementation of this would be, in my opinion, a latching relay. That is, a relay (read "high" current capacity, when compared to transistors) which only requires current to switch its position, but not to maintain the relay in that position. The benefit of that is that even if the alarm isn't receiving power, the engine is still disconnected. Also, it doesn't drain the vehicle's battery to have the relay "activated". I suspect something like that is what is used in the SPY 5000m 2 Way LCD Motorcycle Alarm System. I have a strong preference for how that alarm worked, in that the ignition was always disconnected whenever the alarm was armed, and as far as I know, it didn't take extra current to do so. However since it did not specify what type of relay was used, and the circuit was internal, it is mere speculation.

For the Coban GPS303G used in this Instructable, implementation is a bit more complicated. The "Oil and Power Cut" wire (engine disconnect wire) is simply a wire that is grounded when active. That is, it is supposed to serve as the negative connection of a separate relay. The issue with that is that automotive 12v relays draw around 160mA (0.160A) which is a lot of current draw for tiny motorcycle batteries. Especially when running the GPS tracker simultaneously (another 60-120mA). The result is that you have very little time to actually use the GPS tracker to find your vehicle if stolen (if the vehicle battery is removed or disconnected), and once the alarm's battery is drained the relay deactivates and the engine could in theory be started. I wasn't too happy with that. But it's the best option available for the moment.

While the "ideal" solution would have been to create some sort of exterior latching relay circuit, it would have been bulky and impractical to use on a motorcycle. I went with a satisfying compromise. A Reed Relay. Reed Relays are very efficient, very reliable, and very long life versions of "normal" electromagnetic coil relays. They are actually very similar (wiring is essentially identical). But in exchange for the prior advantages, they tend to have a much smaller current carrying capacity. In this case that won't be an issue, making it the perfect simple solution.

The type of relay required is a NC, or Normally-Closed relay. Like the name suggests, the contacts are normally closed and when the GPS Alarm triggers the remote disconnect, the contacts open disabling the engine. The specifications we were looking for are 12v, Normally Closed, as much current capacity as possible, and as low current consumption as possible. The best I could find was the JWD-171-19 Reed Relay from Tyco/Potter & Brumfield.

In contrast to the 150-200mA of current consumption for normal automotive relays, this reed relay consumes only 10ma with its 1200 Ohm coil. They cost around 5 to 10$ per unit, and seemed to be perfectly suitable. The spec sheet can be found here. However any similarly specced reed relay would also be suitable. I chose that model based on availability and price. If anyone knows of a more suitable, cheaper model, post it below. Also, I'd imagine that doing this with transistors would also be possible, but it wasn't something I had enough experience to feel comfortable with.

Now one of the biggest questions remaining is what to wire the (reed) relay to. These were the options that came to mind when first thinking about the issue, and what I found out on further inspection:

Ignition Fuse

This is the go-to option for most people. Just wire a relay inline with the ignition fuse wiring. I've done this method before, but I'm not all that fond of it. The ignition wire is fused by a 10 amp fuse, which at 12v isn't an insignificant amperage. Given the importance of this wire (it directly feeds the spark plug coils), tampering with it effectively voids the warranty on the whole bike, and if the engine starts acting up, you will be suspicious. If you take the bike to a mechanic with an engine running issue, they will blame it on that even if it's totally unrelated (normally it is the weekend mechanic's fault, after all). When I had issues with my Power Commander's firmware (I didn't know it was it's firmware at the time), I was suspicious of the remote engine disconnect wiring. After all, Guardian Bells can only do so much when it comes to electrical gremlins. So while the Ignition Wire is an option, it isn't really the ideal option. The Ignition Wiring Diagram is attached if you want to see how the ignition fuse is wired.

Engine Stop Switch (on the handlebar controls)

When I was considering methods to kill the engine, I originally supposed that the kill switch on the handlebar would be sending a signal to the ECU to kill the engine, opposed to actually being a part of the ignition system. I was wrong. The engine stop switch is inline with the Ignition Fuse, and as such has a 10 amp fuse ("carries up to 10 amps"). It also feeds the ignition coils directly. In case you're wondering, I haven't found an exact figure for how much current the ignition coils consume at 12v, but it's around the 5 amps range (less than I suspected).

In any case, wiring the remote engine disconnect to the engine stop switch is effectively identical to wiring it to the ignition fuse, giving it the same disadvantages of a "high" current wire.

Vehicle Down Sensor

This was a bit "outside the box", but given that most modern motorcycles have a vehicle down sensor that when tripped, turns off the bike, it was an option.

The way it works is that if the bike's ECU detects it has been dropped, it kills the bike until you turn off and on the engine with the bike upright. If you could trick the bike into thinking it's laying on it's side perpetually, you could in theory keep the engine from running. However after studying the service manual, I found out this isn't an "either 12v or 0v" sensor. The vehicle down sensor's output works on 5v, and it's output varies between 3.55-4.45v when the bike is upright, and 0.65-1.35v when the bike is down. I would guess that substituting that output for ground may very will suffice to trick the bike into thinking it's down (or you could simply feed the correct voltage with a voltage divider), but I was beginning to realize that it wasn't going to be the best option.

Another issue I had with this method is that the ECU may very well store a counter of how many times the vehicle down sensor has been triggered. Or it might use the angle value for other type of metrics (ABS perhaps?). It's mere speculation on my part, but regardless, messing with it proved to be an unnecessary hassle.

Kickstand / Sidestand Switch

Personally, I ended up going with the kickstand switch. It was easier and less current-carrying than the kill switch, and it would be horribly nightmarish for a thief. Even if you introduce some resistance because your connections aren't that great, you're never going to be able to make the ECU read the wire as the other state. In other words, it won't affect how the engine runs, nor give you problems. If your bike starts, the remote disconnect circuit is working. If it doesn't at all, then you might have an issue.

If you wire a relay to the the kickstand switch, making the alarm simulate the kickstand being down, it will allow the thief to start the engine in neutral, but it will kill the engine as soon as he puts the bike in gear. If they put it into neutral again, it starts, but then it will die again once in gear. Imagine how incomprehensible that would be when you're nervous and racing against the clock! I'd also like to think that by allowing the bike to run in neutral that would at least give a few more minutes of runtime to the GPS alarm by allowing it to charge. Not much, but it certainly doesn't hurt.

So that's why I ended up going with the Kickstand Switch for the Remote Engine Disconnect. It was the best choice. It was also the closest to where I installed the GPS Alarm, so I'd need the least amount of wire to hide. Another reason was that I thought how amusing it would be if someone stole the bike, somehow hotwired it, but then could get it to start but every time the vehicle was put into gear, it would turn off. That would be extremely weird from the perspective of any thief.

*Note to self: While this tutorial was written regarding a 2015 Kawasaki Ninja 300, it was written while installing a similar alarm on a 2017 Kawasaki Ninja 650 (for which no shop/service manual was yet available). Comparing the shop manual of the 2013 Kawasaki Ninja 300 and the 2013 Kawasaki Ninja 650 (shop manual years, not vehicles), some differences in wiring were noticed between both models, which could have been presumed to be similar. In the 2013 Kawasaki Ninja 300, the fuel pump relay is triggered by the ECU, whereas in the 2013 Kawasaki Ninja 650 it is triggered by the Ignition fuse/Engine Stop Switch. This means that the shop manual of your specific motorcycle should always be consulted prior to making any assumptions, since the circuit may be different even for similar models from the same brand.