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Discussion Starter #1
Hi,

My 2008 Solstice doesn't have the factory alarm or RKE, so I'm adding an aftermarket alarm. I know the door switch is integrated in the latch on these cars, so I need to figure out where to connect the wire for the door trigger. From searching here it appears that the grey wire in the BCM in the passenger footwell is the ground for the lights when the doors open. Would this be a good place for the door trigger wire? Here's a picture of the grey wire from the footwell lighting thread.

 

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It depends on how well your alarm will tolerate the PWM control provided by the BCM. The grey wire supplies the ground for the courtesy lights, and fades them out before turning them off. This varying signal may or may not cause a problem for you.

The door ajar switches are wired to terminals 19 and 22 on connector C1, the one that is above and parallel to C3, which you show unplugged. The wires are tan/white and grey/black, and come from the RH and LH doors. You would have to be careful with those as well, to ensure that your alarm does not cause a problem with the BCM.
 

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Discussion Starter #3
Thanks. By "problem" do you mean it might not work correctly or it might damage the BCM? I guess the door switches would be better than the ground, except that if I connect both of them to the alarm I'm defeating the purpose of having separate switches. I'm guessing this could also damage the BCM?
 

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You should be OK with the BCM and connections to C1-19 and 22. I used them (well just 19 actually) for my radar interior motion sensor setup to trigger the built-in car alarm if someone gets to far into the car (level 2 alarm). Just decoupled it with a diode. These connections work as active ground - i.e. they are grounded through the switch in the door when the door is opened.

More details on my setup here: http://www.solsticeforum.com/forum/f62/success-installed-my-interior-motion-detector-66229/

...and more photos in here: Success! Installed my Interior Motion Detector (with info...)
 

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If you are just connecting input to the alarm to the door switch wires, you may not even need diodes. But, it can't hurt. You can use use pretty much any old small signal or rectifier diode. The old standby of 1N4001 will be good (or 1N4002,3,4,5 etc) - bound to have at least one of those at RadioShack.

Place the diode between your alarm wire and the splice with the door switch wires, with the band on the diode on the door switch side.
 

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The diode installed as described will protect the alarm system from the BCM, but not the BCM from the alarm. For full protection you should install a diode in each wire from the BCM as well.

If you connect a diode as TS described between the alarm trigger and each switch wire (two diodes), they will isolate the switch wires from each other and allow either door to trigger the alarm.

Assuming that everything is operating at the same voltage, it is unlikely that anything will damage anything else. The most likely "problem" is undesirable function, and that is fairly unlikely too.
 

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Discussion Starter #8
Thanks, that's what I was concerned with. Unlike my old cars where the door circuit is a single loop, the BCM reads which door is open. My concern was that if I connected both door wires from the BCM to the single alarm trigger that the signal would cross to the other circuit. I'll try a diode on each line spliced to the single alarm trigger and post how that comes out.
 

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Yes, I wasn't clear, as I reread my post, about needing two diodes. Thanks to JR for clarifying my intent :)
 
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