Switched earth to relay?

[qwea44]

Hello folks,

So my van got found after being stolen ;D
Now I'm installing my own alarm on the van which is triggered when a door is opened.

Im stuck with this though;
for the open door trigger i need a 12v when the door is opened (Or 12v when door is closed)
I attached the switched earth cable from the cabin lights to a relay. And on the other end a solid 12v positive.


The relay should now give 12v when the door is opened which it does. But when i close the door it gives around 2/3 volts instead of 0. So my alarm device doesnt recognise the door is closed because it has to be 0 instead of 2 volts.
Also i hear a very loud buzzing noise from the relay for 1 second when i open the door. I worked with relays before and never had this. Normally its just a click

What am i doing wrong Can i fix it with a diode or a resistor or something, so it gives 0 if its below 9 volts?
Any help is very much appreciated.

Barry

 

[UNG]

The problem with vehicles these days is all the ECU's they have, while it may be possible to use pull up / down resistors or diodes to fix your issue it may cause other issues with an ECU or multiple ECU's

 

[qwea44]

The problem with vehicles these days is all the ECU's they have, while it may be possible to use pull up / down resistors or diodes to fix your issue it may cause other issues with an ECU or multiple ECU's

Thanks for your reply. But if i place a resistor on the output post of the relay, would that even affect the ecu? As it has gone through a relay already. I dont think so but im not sure. Do you know what kind of resistor i would need for this?I just dont understand how the switched earth cable is reading 0v and the positive wire 12v but the relay outputs 2.3v

 

[Avo Mk8]

When you switch off the 12v, presumably the input to your alarm floats to whatever its circuit determines.
If you used a relay with changeover contacts, you could have one pole at 12V and the other connected to 0V, so it would switch from one to the other.

Playing with resistors on the output of the relay will surely not interfere with the ECU or can bus, there is no connection to those at that point.
You could try a pull down resistor of say 1k ohm across the alarm input, and see if it thinks that is "0V"

 

[mainline]

Hello folks,

So my van got found after being stolen ;D
Now I'm installing my own alarm on the van which is triggered when a door is opened.

Im stuck with this though;
for the open door trigger i need a 12v when the door is opened (Or 12v when door is closed)
I attached the switched earth cable from the cabin lights to a relay. And on the other end a solid 12v positive.


The relay should now give 12v when the door is opened which it does. But when i close the door it gives around 2/3 volts instead of 0. So my alarm device doesnt recognise the door is closed because it has to be 0 instead of 2 volts.
Also i hear a very loud buzzing noise from the relay for 1 second when i open the door. I worked with relays before and never had this. Normally its just a click

What am i doing wrong Can i fix it with a diode or a resistor or something, so it gives 0 if its below 9 volts?
Any help is very much appreciated.

Barry

Is the cabin light a lamp or an led ?