I've spent quite a bit of time thinking about this. Landcruisers are one of the most stolen vehicles here in Australia, and my HZJ80 is all mechanical. There are literally only two electronic things you can do to prevent this car starting: interrupt power to the starter, or turn off the fuel cutoff solenoid in the back of the injector pump. I've wired a kill switch to the fuel cutoff solenoid, while keeping the glow plug relay and starter working, that way a potential thief won't see any indication there's anything wrong until he tries to crank the engine, at which point it'll make a lot of noise but not fire, drawing attention. The thing is though, because anyone who actually knows these cars will realize that's all I could have done electrically, the kill switch will only stop an uneducated, opportunistic thief. For that reason, I don't have any qualms about posting some info about it here. Let's play a game: spot my kill switch:
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It's hiding in plain sight, and if you know these vehicles, I've already told you everything you need to know to figure out where it is. Who can pick up on it?
Now, because as I said, a kill switch is only going to stop opportunistic, uneducated thieves, and with the price of these things going up and up, I need a backup. That's why I have an old android phone with a "find my phone" tracking app and a prepaid sim embedded in the chassis, on a permanent soak charge from the aux battery, and days of charge even if that goes dead. If someone's dumb enough to steal my rig, I'll pull up the tracking history and know exactly when they took it, where they went, and where they are now, at which point I'll walk down to the local police station and see if anyone is interested in getting credit for taking a drive and busting whatever chop shop they've taken the thing to. Costs me about $15 every six months in credit to maintain. Pretty cheap insurance IMO.