Possible Negative Trigger for Car Alarm

Hi All, I have a question about a possible negative trigger for a car alarm. First, back story my catalytic converter was stolen from my 2010 Dodge Ram 3500 while parked in my driveway. I will be installing an AutoPage RS915 this weekend and would like to know if wiring the negative trigger for my hood/trunk as shown in the diagram will work for triggering the alarm when catalytic is tampered with (hopefully it uploaded! It was my first time using MS Paint!!) I know that I will probably need to use a diode with it but not certain as to where to put it exactly, I'm thinking it will need to be placed on the Ground While Armed wire. My thoughts were to use the GWA wire to active the first relay and use the ground from the catalytic to complete the second relay...when wire is removed from catalytic it will cause the relay to lose power and 30, which will be my hood/trunk trigger, to connect to 87a which will wired to the GWA causing the alarm to trigger.

I have also kicked around idea of putting a sensor near the converter but not sure how to waterproof it or keep stray cats from setting it off by walking underneath my truck. Any and all thoughts will be appreciated because this is probably an unconventional trigger.

That will run your battery down if not driven daily. Try this, use the positive trigger wire of the alarm and wire as follows. At the alarm brain, wire connect a 1000 ohm resistor to the constant power input of the alarm. Connect the other side of the resistor to the positive trigger wire of the alarm. Connect the positive trigger wire of the alarm to the catalytic converter. If the cat is removed, or ground is removed from that wire the resistor will make the wire go positive which will trigger the alarm.

Adding to IAAI's post. The alarm module may allow the value of the resistor to be increased, while still being an acceptable trigger input.
No need to place additional draw on the battery. Also Directed/DEI has a closed loop trigger module (502T) which reduces the draw significantly.

You should only need one relay to convert the signal - ie, from ground loss to make a ground, ie, signal inversion using an SPDT relay.
However that method means the relay is normally energised hence discharging your battery.

Surely there is some +ve edge alarm trigger - eg, a pull-up resistor so that a cat ground break changes the line from GND to +12V?

Otherwise I'd use a FET or transistor. That's a nA or uA draw compared to 50mA or more for a relay.


PS - I missed the above 2 replies. Not sure if that was due to another strange timelag issue or if that's when I got that phone call...

The problem I see with your system is that by the time the ground is lost, and the device triggers, it's too late. The cat is already off the truck.

Probably more effective to come up with a physical barrier to protect the cat. There are all kinds of devices that limit access and make it more difficult (takes more time, something no thief wants to do)to cut the cat off the truck.

The guy up the street made a "grill" out of 1/2" square steel tubing that bolted to the cross members under his Forerunner to "cage" the cat in. Still allowed air-flow cooling, and was removable for service, but a very visible deterrent. Took him an afternoon with is mig welder and $25 in material to make.

You want something the thief will see right away, and he'll say "f this, I'll find another one".

First and foremost, apologies for not responding sooner, work and life got in the way! I was able to install my 915 and could not be happier with it..that being said...

IAAI- Thank you, I was worried that my poorly designed relay would draw too much..although I have 2 batteries in my diesel- sometimes my truck will sit 10-15 days at a time without being driven.

Ween- Thank you for your suggestion on the 520t, I thought I had researched all possible sensors available, but I was not aware of this one.. I did order one and it should have been here weeks ago but still has not been delivered--should be here soon though!

Old spark-- Appreciate your input!

davep.-- I did forget to mention on my original post that my catalytic is actually easily removed by 6 bolts- (3 in front and 3 in rear)..unfortunately I do not have access to a welder but your suggestion did inspire me to take my truck to the local muffler shop where they were able to tack weld the hex nuts for $15 (money well spent!!) So hopefully if the would-be thief crawls under my truck again he will see the welds and say "There's got to be a better way..." and move on down the street.

Again, thank you all for the great replies. All of your input really steered me in the right direction and you can officially consider my problem solved!

Forget the 520t incidentally I use DEI product on Sprinters where you can change the trigger to NC and run the trunk wire down to a bolt holding the catalyst, BUT the weld idea was much better!!

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

howie- Just out of curiosity which DEI product are you using on the sprinters where you can change the trigger to normally closed?

330X series and up, you can switch the triggers individually from normally open to normally closed. On 07 on I use a DB-ALL 2 for door triggers etc. with the blue trunk trigger down to the cat and programmed as NC. Originally designed for Fords and Mazdas with NC triggers but works just as well on cats.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.