How can I put an Audible warning on an immobilizer?

[buzzer]

We have had quite a few cars stolen around here in the last few months, all of them have been older cars… a 1992 Civic, an old Triumph 2000, two MK1 MX5’s that I know of personally. Seems the older easier to start cars are being targeted.

I already have an immobilizer switch wired into the fuel pump on my MX5 and our old Corolla, along with an alarm, but my wife keep forgetting the throw the immobilizer switch.

Anyone know how I can wire a buzzer in so that if the ignition OFF and the Immobilizer switch is still closed, the buzzer sounds?

Here is the basic diagram where 1 is the ignition switch, 2 is the immobilizer switch and 3 is the fuel pump.

[buzzer]

Mr2Mike said:

Simply connect the buzzer across the immobiliser switch. They draw very little current so will ground through the fuel pump without actually powering it. Watch for polarity on solid state buzzers.

nice simple solution if this is what you mean... my only problem with that is that on AUX the buzzer will be going off which will be annoying if you just want the radio on...

[buzzer]

will this work? instead of using a buzzer , I use a relay (4) wired in as below. the switch (5) is now a spring loaded one. So each time you get in you have to turn the ignition on, hold the switch for a second and release. this pulls the relay in and the loop back holds it there until the ignition is switched off.

Thoughts?

[buzzer]

ch427 said:

as said that circuit would run the fuel pump all the time as it is until the ignition is turned off which may be an issue.

Not sure what you mean by this?

[buzzer]

ch427 said:

Most pumps run for a few seconds and then stop at initial start up when the system reaches pressure,you may damage the pump if its running for too long as per the diagram depending on pump type.

Maybe I am missing something? the way its wired anyway means there is a constant live feed to the pump when the ignition is on. All the relay does is hold the current on until the ignition is switched off?

[buzzer]

Mr2Mike said:

I actually meant for the buzzer to be connected across switch 1 which at first glance gives the desired operation. However I just read your OP again and noticed switch 1 is the ignition switch, so presumably the wire connecting switch 1 to switch 2 also feeds numerous other circuits, in which case it won't work!

If that is the case the easiest way to make this work is to replace the immobiliser switch with a double pole switch. One pole would be connected the same as the current single pole switch, one side of the the other pole would connect to the pump +ve and the other side would connect to buzzer -ve, and buzzer positive would go to battery +ve.

With ignition off and immobiliser switch on, the buzzer grounds through fuel pump and sounds. With the ignition on, the pump +ve is at (more or less) the same potential as the battery, so the buzzer has close to zero voltage across it and switches off.

Thanks mike, I see what you are saying I think... if you mean like this, where 2 is a double pole switch, the only problem I see is that I cant use the AUX position on the ignition.

[buzzer]

Now this would work.... a double pole switch (2) that reverses the contacts when you switch it over. Shown here in the running position.

Unfortunately I cant find a switch that does this!

[buzzer]

Mikey G said:

buzzer said:

Now this would work.... a double pole switch (2) that reverses the contacts when you switch it over. Shown here in the running position.

Unfortunately I cant find a switch that does this!

You are making this awfully complicated, and that wont work as you are turning the buzzer on when turning the immo off

Are you sure?

[buzzer]

Mikey G said:

buzzer said:

Are you sure?

Well in that drawing yes, current state is fuel pump on buzzer off, if you throw the switch then your turning the fuel pump off and the buzzer on

you are right

[buzzer]

Mikey G said:

I want to know this drawing program you have as it looks handy

The programme is Microsoft Visio, it's a great programme used for all sorts, it has mechanical symbols, all electrical, plumbing, even garden and kitchen design! I used to use it at work for process mapping on business redesign.

some examples, out kitchen plan, and garage plan. I had a Caterham at the time

Edited by buzzer on Saturday 23 November 11:51