Help with alarm trigger mod

[Mike1220]

So I have determined that this mod will probably no longer be able to done easily using existing factory theft deterrent.

 

The current door and hood sensors are powered and always sending a signal to the BCM that shows a status.

Disconnecting the switch is recognized by the BCM as a fault condition so the anti theft system will not initiate.

Any approach I might try using a standard open or close type switch will not work into this circuit.

 

So I am at a stand still. The only possible way to do this might be to duplicate the current sensors at each door and place them so they are triggered by the handle pull. And I can't figure out how that might be connected - series? parallel?

 

Probably the only way to do it would be to add a second alarm to the vehicle that accepts ground pin type switches.

 

Since I see no easy way to move forward will have to drop this for now. If anyone has any suggestions please let me know.

 

I'm not too keen on this kind of thing but would a pressure switch work? Kinda like the ones you see in movies where once pressure is removed it sets the alarm?

 

If you wire the door handle in to the hood sensor so that the pressure switch will keep it engaged (when handle is in normal rest position) and then the switch initiates the fault and sets off the alarm? A momentary switch may work as well

Not sure if these are thoughts you've had and may try but it was some random ones I thought of while reading your last post

[Jackseric]

The current door and hood sensors are powered and always sending a signal to the BCM that shows a status.

 

 

So they're always sending a signal... must be a certain voltage, that changes when triggered, correct? Is it a voltage drop, like it's been disconnected, or does the voltage increase?

[crewl1]

 

So they're always sending a signal... must be a certain voltage, that changes when triggered, correct? Is it a voltage drop, like it's been disconnected, or does the voltage increase?

I will have to confirm as I did not note which way it went . When I was first testing the hood switch I was looking for continuity, but noticed a change in resistance from the switch. After that I tested just the harness that goes to the switch and found it was a 12 v feed into the switch.

I kinda stopped there as I was confused and afraid if I messed with it too much I could get an error code on the module so left it.

What I did find was that if I disconnected the switch and tried to arm the alarm, the indicator would fast blink just like when the hood is open.

I will check this evening to confirm.

I only have a multimeter so not sure if it is safe to do this?

From the hood switch there are three leads coming out, but the harness plug only has wires from two of the three contacts.

To get an accurate read , where should I be attaching my probe?

[crewl1]

I'm not too keen on this kind of thing but would a pressure switch work? Kinda like the ones you see in movies where once pressure is removed it sets the alarm?

 

If you wire the door handle in to the hood sensor so that the pressure switch will keep it engaged (when handle is in normal rest position) and then the switch initiates the fault and sets off the alarm? A momentary switch may work as well

Not sure if these are thoughts you've had and may try but it was some random ones I thought of while reading your last post

I originally planned to use a lever momentary switch as tis is what I have used in the past to have the handle pull action bump the lever.

The switch would just sent a ground signal when depressed.

I don't think a simple ground switch will work here though without some other device .

[Mike1220]

I originally planned to use a lever momentary switch as tis is what I have used in the past to have the handle pull action bump the lever.

The switch would just sent a ground signal when depressed.

I don't think a simple ground switch will work here though without some other device .

 

 

but what I'm saying is since it has a constant signal, why not run the switch with the signal, then when the door handle is pulled then the switch is released, causing it to drop voltage

not sure if it would work.

[crewl1]

 

 

but what I'm saying is since it has a constant signal, why not run the switch with the signal, then when the door handle is pulled then the switch is released, causing it to drop voltage

not sure if it would work.

Ok I Think I understand - I interrupt the power to the hood switch using my additional one that is normally closing the circuit.

When the switch gets pressed it opens the circuit breaking the connection and the BCM sees a change in status.

OK let me test that this eve.

Thanks!

[crewl1]

So I tested the approach above, and what I found is that it does trigger the alarm when the circuit is broken, but for some reason the break has to last more than three seconds.

(I believe this may be to prevent the system from triggering on faulty connection.)

 

Momentarily breaking the circuit will not trigger the alarm unfortunately, which is the desired case since we cant expect t a bad guy to stand there and hold the door handle for an extended period of time.

 

Later today I will see if I can figure out the differences in voltage coming out of the switch.

[crewl1]

Testing for voltage this is what I find:

 

With the harness disconnected from the switch the wires show 12v + and ground

 

Once I plug in the switch, the same wire that showed 12V now shows 6v+ when the hood is latched, and 3v+ when the hood is popped.

 

So to be able to do this mod I would have to be able to send the correct voltage to the BCM replacing what the switches show in their normal state.

 

I don't know really anything about car electronics so don't know how I could do it. The hood latch switch is a very small device, and actually I have not removed it to inspect it since I have not disassembled the hood latch itself. I will have to do some research on how these sensor systems work.

 

I think a clue is the connectivity to ground I noted earlier. Would a resistive load to complete the ground circuit do this?

 

If anyone has any info on the switch itself like a part number that would be welcome.

[Mike1220]

so the alarm wouldn't trip if it saw a complete break in the voltage? i.e., if you wire the switch to normally carry the current and then pulling handle would break the circuit, this would simulate someone cutting the wire for the hood latch. I would think that would trip the alarm but Ive never messed with the security system on a vehicle

 

well, unless you count taking an old 65 car (it was a mustang or camaro, don't remember, it belonged to my buddy's dad) with a big block V8 and we set some car alarms off in the parking lot cause the exhaust was that loud

[crewl1]

so the alarm wouldn't trip if it saw a complete break in the voltage? i.e., if you wire the switch to normally carry the current and then pulling handle would break the circuit, this would simulate someone cutting the wire for the hood latch. I would think that would trip the alarm but Ive never messed with the security system on a vehicle

 

well, unless you count taking an old 65 car (it was a mustang or camaro, don't remember, it belonged to my buddy's dad) with a big block V8 and we set some car alarms off in the parking lot cause the exhaust was that loud

It does trigger if the break lasts more than 3 seconds.

 

That would be fine if we could use a resettable toggle of some sort.

 

To date I have only used momentary switches and a handle pull only lasts a second at max travel.

 

One second of a complete loss of signal isn't enough to make the alarm sound.

 

On the other hand, the factory switch triggers the alarm immediately.

[DAP56]

My 2003 Hummer H2 and 2006 H2 SUT both had this. You pull that handle when the car is locked and you are getting horn in your face.

 

 

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[DAP56]

The thing I liked the most is that the doors and tailgate would open part way to really mess with the would be criminal.

Just as they thought they were in, the door would catch and horn would fire.

 

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[Mike1220]

you know, that wouldn't be a bad idea, hook the door handles up to a momentary lever switch that triggers the horn, that way as long as the handle is pulled the horn will sound. I mean, thats pretty much all that the alarm will do plus flash some lights. Wouldn't be hard to activate the lights as well, just wire into the respective relays and use a diode to prevent back feeding

[jmorzuch]

Tying into the hood switch may be an option if I don't find a way to use door switches.

The hood catch has a set of wires coming to it and it will trigger the alarm when the hood release is popped, so one or a couple of those wires will work.

 

I'm probably not going to get to this until I pick up the Pop n Lock for the tail gate and I will do it all at the same time so it may be a while.

 

If anyone wants to get a jump start on their own project the switches that I have used in other vehicles are called Micro Lever Momentary Switches and look like this:

The bottom lug is common and the others are a normally closed and a normally open lug.

For a switch to ground, you would wire the common lug to the alarm trigger input and then wire the normally open lug to a screw on the chassis.

 

You place the switch lever so that when you pull on a locked handle it pushes the lever against the button on the switch and makes the ground.

 

These switches have two mounting holes that you can run a zip tie through to position it where needed, or because they are a flat body you can also use good quality double stick mounting tape to place it in the door.

 

You can also find these with extra long levers that you can bend into the right position to meet with the handle motion.

 

It might be a while before I get to it but when I do I will document it with pictures for folks to see.

 

You wouldnt need to do the hood because they have to open the passenger door to get to the hood release, at which point the alarm will already be going off

[crewl1]

 

You wouldnt need to do the hood because they have to open the passenger door to get to the hood release, at which point the alarm will already be going off

No the point is that I want to use the hood switch as the trigger point to the BCM for someone who just tries the handle on a locked door.

I have ordered some 700 ohm resistors and if I can get this to work I will update the thread.