Failed DIY. Help needed!

[Equinox1]

Some one is in a habit of stealing petrol from my car.
Decided to do A DIY. Had a spare magnetic door sensor which uses a reed switch (wired part) and a magnetic part(non-wired part) to sense & trigger

Therefore decided to rivet the door sensor to petrol lid & connect its wire to door push button which switches the cabin lamp "on" & "off".

PROBLEM:

The door sensor works(alarm activates) when the magnetic part(non-wired part) is bought near the reed switch (wired part) where as it should do the opposite. i.e. the alarm should activate if the two parts of sensor are not in close proximity to each other.

I have also reversed the wiring contacts but the result is same.

I have searched on internet & found that security systems use a state called Normally Closed (N.C.), therefore if a someone cuts a wire the security system goes into a "Open" position and it triggers the alarm.

Therefore I ASSUME that I need to convert it into a default Normally Open (N.O.) state but dont know how to do it.
Any sort of help in this regard will be appreciated.

[Equinox1]

@capsat @xulfiqar

[Hashim11]

You need to use a relay. It has NC (normally close) and NO (normally open) states.

[Equinox1]

@Hashim11 can you please elaborate further with pictures.

which relay? where should it be connected? etc

[capsat]

I have never worked on car security systems so I have no idea about wiring configuration. Though if you want to activate an alarm from unlatch position the other end of latch shall be linked to alarm power, so as soon as the latch is OFF HOOK the alarm is ON. when latch is ON-HOOK the power to alarm shall be OFF. - the latch shall be powered from an active 12V DC means a wire running directly from battery or from fuse box, not from any door switch or stop lamp or accessory source.

[Hashim11]

There are two types of reed switches, NO and NC. You are using wrong switch, use the switch which is Normally close, so that when you close the door, reed switch will open (alarm turns off) and switch will close (alarm turns on) when you open the door.

[shabbir.1]

There are two types of reed switches, NO and NC. You are using wrong switch, use the switch which is Normally close, so that when you close the door, reed switch will open (alarm turns off) and switch will close (alarm turns on) when you open the door.

The method explained above is the most easiest way to solve the problem. You can find another switch from Karachi Cooperative Market.

This is perhaps the circuit of how you have wired the reed switch.

If you want to keep the existing N.O. switch then you have to insert a N.C. relay in between the switch and the alarm.

[Equinox1]

@shabbir.1 any idea of what this N.C. relay is called when purchasing from the market? the "desi" term

[shabbir.1]

@shabbir.1 any idea of what this N.C. relay is called when purchasing from the market? the "desi" term

It is sold in the market on number of pin-outs and the coil voltage. E.g., 5 pin replay is a single pole relay with both N.O. and N.C. contacts (2 for the coil, 1 each for N.O. and N.C. and 1 is common) 8 pin relay is a double pole relay i.e., with two sets of N.O. and N.C. contacts.
It will be much better to use any spare automotive relay due the fact that they are rugged, mostly sealed and the coil is designed for the 12VDC.
Which car do you have? Has the security/keyless entry system got the option of trunk latch trigger. If this option is available in the security system then you can even utilize it for this purpose, this way you won't need an extra alarm in your car.

[Equinox1]

@shabbir.1 I think I have a spare denso horn relay like shown below. will it work?

[shabbir.1]

Horn relay! it must be a single pole N.O. type, yes you can use it but where is it its original connector?

[Equinox1]

yes i do have the orignal connector aswell. This is just a reference picture. Will post snaps tomorrow

[Equinox1]

@shabbir.1 The relay has four connections

]2 1[
4 3

Now where should each wire be connected?

[Equinox1]

part no. of relay is 90987-02004

[Hashim11]

Check on relay. like 1 n 3 are for coil power and 2 n 4 is normally open in dis pic.

[Equinox1]

yes its the same.. where to connect 1-2-3-4?

[shabbir.1]

Pin 1 and 3 are for the coil and pin 2 and 4 are the N.O. output contacts. I have placed the pin numbers on the diagram below.

[Equinox1]

[video=vimeo;83209946]https://vimeo.com/83209946[/video]

[Equinox1]

@shabbir.1 @hashim11
I have independently set up the circuit according to the daigram but the results are the same. any ideas now? i want the sensor to do the Opposite of how it is working now

[Equinox1]

@shabbir.1 @hashim11
I have independently set up the circuit according to the daigram but the results are the same. any ideas now? i want the sensor to do the Opposite of how it is working now