How to make a cheap DIY anti-theft device.

Updated: 10 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

what if i just remove it?

You uhmm, i mean, ehmm, that eh. no.

I installed a cut off key switch so the starter relay doesn’t work

BREAKING NEWS: Car thief caught with bag full of relays.

Yea… Good idea except that my fuel pump relay sits behind the glovebox… Which is held in by a lot of screws… Tho i can just blow a fuse and put in the fuel pump fuse position since that fuse is not named fuel pump in any way

Remove any prong and it will not function.

Well, it’s funny that i’m reading this, since yesterday i got robbed. They forced the keyhole of the door and stole some bunch of things me and my friend had there. Luckly i always put the steering wheel security bar, so there could be too damm hard to stole all my car. The annoying thing, is that the robbery happened on a payment parking of a mall center. Goddamit, they have security! That’s why i’m paying!

Nevermind, they don’t take responsability on “minor damages” and “partial robberys”, so the only thing we can do is to report that to the local police and hope for something… or at least they increase the security there, they told us that isn’t the first time that happened. (And btw, we suspect was someone working there, the mall center is still under construction, and there’s a lot of people entering and exiting without being checked.

Anyways, now i’m searching for at least a basic alarm that i can afford, but now that i’m reading this, i’m considering a cur off switch too. It’s just a Spark, but is the only ride i can afford.

instead of f@#king around why not jsut pull the relay and store it taped to the backside of a panel in the dash

gold

How about cats that start with the push of a button like the Suzuki Kizashi, that car does require the press of a button but it also requires the physical remote/key because if you try to press start without the key inside, it will refuse to turn on. So is this post applicable to my parents car? (15 yo btw)

Long story short, yes. How your car turns on is irrelevant unless you have a dedicated track only race car which has a set of switches to turn on power and the fuel pump and whatnot.