Bainzy Posted September 10, 2012 Share Posted September 10, 2012 Today I was working on a car that has an alarm system that activates (or in a sense, deactivates?) an immobiliser when the alarm is triggered:It currently cuts an ignition coil using a 40A automotive relay, and is wired as above.I tried to then get another relay in a different location to intercept the fuel pump feed, and couldn't get it to work without disturbing the operation of the other one. Here's the method I tried that didn't work:It seemed to switch the operation of the existing one, which I didn't want to do. What's the best way around this? I have some diodes I could use if need be. Quote Link to comment Share on other sites More sharing options...
piman Posted September 10, 2012 Share Posted September 10, 2012 Hello Bainzy, in diagram one with 0 volts, terminals 30 and 87A are made, i.e. normally closed. If 12 volts on 85 is normal that breaks the coil circuit, which makes no sense?Maybe I'm misunderstanding how the system works, but you need the coil and pump feed to be connected to 87 not 87A, which will be made with the relay energised. Loss of voltage to the relays opens those contacts and immobilises the car.Alec Quote Link to comment Share on other sites More sharing options...
drofgum Posted September 11, 2012 Share Posted September 11, 2012 Bainzy,Provided that the 87A contact is normally open, circuit 2 looks good, so, perhaps it is to much load for the alarm immobiliser to control. It can be done by using the coil out power to switch the pump relay 86 terminal. Good luck, Paul Quote Link to comment Share on other sites More sharing options...
piman Posted September 11, 2012 Share Posted September 11, 2012 Hello Paul,87A and 30 (common) are normally closed. 86 and 30 are normally open. Yes it can simply be done with one relay by taking the coil and pump feed together.Alec Quote Link to comment Share on other sites More sharing options...
drofgum Posted September 12, 2012 Share Posted September 12, 2012 Alec,That doesn't agree with Bainzy's first diagram which makes it clear that 85 and 86 are the relay coil terminals and 30, 87, and 87A are the contacts. In the first diagram 30 and 87A are used as a normally open contact which closes when the immobiliser is not triggered and thus is still sending 12V to the relay coil at 85.All the best,Paul Quote Link to comment Share on other sites More sharing options...
Bainzy Posted September 12, 2012 Author Share Posted September 12, 2012 Thanks guys. I think the reason it's done like that Paul is so that if you yanked the alarm power out, the relays would then link 30 to 87, thus activating the immobiliser.Load issues would make sense (I think?), especially since the wire used for the immob is proper tiny (the designers can't have been expecting much load to be placed upon it). Quote Link to comment Share on other sites More sharing options...
piman Posted September 12, 2012 Share Posted September 12, 2012 Hello Paul, in relay convention, 30 and 87A are normally closed, which is why I said the circuit didn't make sense.See diagrams here:- http://www.vehicle-wiring-products.eu/VWP-onlinestore/relays/relays.phpAlec Quote Link to comment Share on other sites More sharing options...
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