DIY classic car immobiliser

Over the last 30-odd years the level of security built into cars has skyrocketed. Without having the right key, or a lot of time and electronic ability, thieves find stealing modern cars difficult. But that’s sure not the case for older cars. So what if you have an older car – an outright classic or simply an car you like driving for fun – that you want to make less stealable? And especially less stealable to an opportunistic thief?

Well, for less than AUD$10 and 30 minutes of your time, you can now add a remote control immobiliser to your older car.

The system

Available on eBay for just AUD$5 plus postage is this electronic remote control switch - including postage to my Australian address, the total was about $9! It’s perfect for use as a remote control immobiliser.

The key remote has a single pushbutton on it, while the associated box contains the receiver and a relay output.

At the time of writing, the module plus remote was being sold on eBay by ‘windeal’ and the vendor called it the “12V Multi-function Learning Remote Control Switch New”. You can also find very similar devices available from other eBay sellers.

As with a lot of items sold cheaply on eBay, the instructions are less than comprehensive. But that’s OK – here how it works out.

Inside the receiver box you’ll find a small circuit board with a few LEDs, a configurable link and a 5-terminal strip.

The functions of the important bits are as shown here.

By changing the config link position you can set the device in the following ways. (Note that this is with the board orientated as shown in this diagram and viewed from above.)

·       No link – relay closes and green LED turns on only when remote button is being constantly pressed

·       Link set to left  - relay closes and green LED turns on when remote button is pushed once, then stays on until power to the receiver is removed

·       Link set to right – relay closes and green LED turns on when remote button is pushed once, stays on until button is pushed again

Having these different configs available makes the unit very useful.

Wiring

To disable the car, you’ll need first to decide on a wire that, if broken, will stop the car starting. A further caveat is that unless you add another relay, that wire should pass less than 10 amps when the car is running. (The remote receiver’s relay is rated at 10 amps.)

The wire you choose to intercept could be to an electric fuel pump or the ignition coil.

In the case of my 1979 Mercedes, I chose to disable the ignition coil. Furthermore, I mounted the receiver module under the bonnet and powered it from the wire I was disabling – an approach that made the wiring very simple.

Here are the steps:

1.     Set the config link as shown – this means the relay will pull-in when the remote button is pressed and will stay latched until power to the unit is removed.

2.     Find the 12V feed to the coil. Note that if the car uses a ballast resistor, you will need to work ahead of the resistor as shown here.

3.     When the relay closes, the ‘common’ and ‘normally open’ connections are joined, so as shown here, when the relay is closed, power gets fed to the ballast resistor (and so then to the coil).

4.     Power for the module is gained from the ignition-switched 12V source feeding the ballast.

5.     You need to add a new ground wire for the module – connect this to the chassis.

Wired in this way, the steps in starting the car as follows:

1)     Turn ignition key until dash warning lights are lit

2)     Press remote button

3)     Turn key further to start engine

Note that pressing the remote with the car switched off doesn’t do anything – rather deceptive for a thief! Note also that you don’t need to press the remote button to activate the immobiliser when you leave the car – as soon as you turn the ignition off, the relay automatically opens.

Here are the coil (black arrow) and ballast resistor (yellow arrow) in the Mercedes.

The power supply lead to the ballast resistor was parted at the terminal and extensions put in place to connect to the immobiliser module.

A ground connection for the immobiliser module was made at a convenient screw (and later I moved this to an even more convenient screw!).

The fitted system, with the receiver module arrowed. Seal the module’s box with some neutral-cure silicone.

If you wished to, you could disguise the writing by concealing it within the loom, so making it harder for a thief to find. You could also place the immobiliser module inside the cabin – the system has many tens of metres of radio range, so that won’t be a problem.

Conclusion

A DIY, remote control immobiliser doesn’t get much cheap or easier than this!