How to make a cheap DIY anti-theft device.

09 Dec 2016

One fear car guys constantly have in the back of their mind is getting their car stolen. That’s why there are plenty of different anti-theft systems out there, but they can clear out a bank account pretty quick. There are also other methods of keeping your car from being stolen, such as installing a fuel pump cut off switch. However, if time and/or willpower is not of the essence, there is a very simple way to keep thiefs from stealing your pride and joy, and very cheap if you happen to find one in your local salvage yard: a defective relay.

If your fuel pump relay goes bad, replace it, but keep the old relay. That relay can be easily installed in place of the good one, and when any thief tries to start your car, the only thing that will happen is your car will turn over but it will not start. With no power going to the fuel pump, there’s no fuel for the spark plugs to ignite, and nothing happens. If you don’t have a bad relay, I’ll show you how to make an anti theft relay using one you may find in the salvage yard.

Step 1: Locate the relay

The first thing you need to do is find out where your fuel pump relay is located on your fuse box. Once you find it, remove it.

Step 2: Find the power

You’ll need to figure out which prong is the one that receives power when the key is turned. The easiest way to do this is to use a test light. Clamp the ground wire onto a suitable ground (I usually clamp it to the negative post on the battery), and with the key out of the ignition, probe each one of the holes that the relay prongs go into, and memorize which ones don’t have power.

Put the key into the ignition and turn it to the “on” position. Then go back and test the prong holes again.

The one that lights up your test light that didn’t before is your power. Now take your anti theft relay, and locate which prong plugs into the power hole. Now for the final step…

Step 3: Break it

Take the power prong on your soon-to-be bad relay and start moving it back and forth until it snaps off. Now that the relay has no way of receiving power, it will prevent your car from starting when installed.

This is a good anti-theft device for when you’re gonna be away from your car for a while, especially if you’re out of town and in an unfamiliar area. Though it’s not nearly as convenient as a cut off switch, it’s very simple and does what you need it to do: keeps the car from starting until you want it to.

Comments

So you break your relay and want to replace it every time you want to start the car?

I think you’re supposed to have 2 relays… 1 good, 1 bad and switch between the two.

I think you’re supposed to have 2 relays… 1 good, 1 bad and switch between the two when you want to start the car.

Just waiting for DisklokUK to comment

stopped reading to look at a cheeky Disklok UK

Personally, I used to just remove the fuel pump relay from under the hood and keep it in my pocket while I’m away… I don’t think there’s a lot of chances that a thief might come to steal my car and happen to have a fuel pump relay in his pocket….. He would almost deserve to get away with it! :p

Another idea would be to just install a switch on the control side of the relay and hide it somewhere.

This is true. There’s a low chance that a thief will search for the missing relay or any sort of cut off. But if he does pop the fuse box, there’s an even lower chance he will try to pop the relay out. Lol

Yep, hé just need à small piece of wire or metal to just active fuel pump.

Good idea. I still think any thief that tries to figure out the problem may notice it and jump the relay and ride off XD

Or just disconnect the battery. I know people living in bad neighborhoods where they remove the battery and take it inside with them every night.

If the thief got a friend and a set of jumper cables it’s still bye bye car. Once the alternator is running you don’t need the battery. You’ll at least get far enough to be safe to steal a battery

Still easier to just take the relay no? The car could still be jumpstarted without the battery

buy a car with a manual transmission

If they’re jacking cars they probably know how to drive a manual

this only works for ‘MURICA

works right up until said thief fries your starter motor. But I have done this with my STi, I remove the relay for the fuel pump when its on my driveway and im out for the day.

I’ll take a busted starter over a stolen car every single time.

Cool technique. I was thinking of a hide away or fold up clutch pedal, so people get in the car (RIP my windows) but then they realize there’s a stick, yet no clutch…

You do know you can drive a manual without a clutch pedal? Start it in gear, it starts hopping a bit and starts. Then you can just shift with a lot of patience and rev matching the gearbox to the engine.

I have a similar setup. My bike uses a ‘fuel tap’, which is, as the name suggests, a tap from the fuel tank, if I open the tap, the fuel flows into the carb, however, I bought a key-operated tap and whenever I get paranoid, I lock the tap to the ‘off’ position and take the key with me.

Where did you bought that? i want one of those for my bike.

do this on a car in the junkyard and wait for someone to part it xD

What my dad used to do when I was a kid was pop the bonnet, take the rotor cap off, remove and pocket the rotor button and then put the cap back on and close the bonnet. It really helps with a carburetored car that can be unlocked with the arm of a pair of sunglasses, a low value coin or anything else that fits