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 Reconnecting a magnetic switch to door frame
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Starting Member

10 Posts

Posted - 05/05/2018 :  3:30:22 PM  Show Profile  Reply with Quote
Our home has an ADT Safewatch Pro 3000 security system, with the front entry door having sentrol magnetic switch ( wired into the door frame (installed in 2009). We had the front door with frame replaced and want to reconnect the sensor to the new door frame. Unfortunately, we didn't think to photograph how the sensor was attached to the wires coming from the old door frame. The sensor has 2 unmarked, seemingly identical white wires but there are 4 wires coming from the door frame (red, black, yellow and blue). Does anyone know which 2 of the 4 colored wires should be connected to the 2 white sensor wires? And does it matter which white wire gets connected with the selected colored wires since they are unmarked and appear identical? Thank you in advance for your assistance.

Advanced Member

800 Posts

Posted - 05/06/2018 :  05:18:00 AM  Show Profile  Reply with Quote
The sensor is just a N/O switch which closes in the proximity of a magnet. I suspect two wires supply DC power (usually 12V) not needed for the reed relay door switch, the other two are for the closed loop.
First, inspect the four wires - you might be able to tell that 2 have never been used. That would likely be the power supply. Otherwise, use a voltmeter to check voltage between wire pairs. I suspect the red and black would be the power, typically showing 12V, while the other pair, being the sensing loop could be at a lower voltage. Alternatively, open another sensor in the system by opening the door or a window, wherever it may be. In that case the loop is open and there should be no or very little voltage on the pair (likely blue and yellow). Those would be the wires to connect the switch to (polarity does not matter). Verify by closing all the doors and windows, then open the newly connected switch and alarm should result.
You may need to play with other color combinations as well, but it's just a few minutes job. Don't try to short any wires while investigating, this will likely blow the control panel power supply or at least its fuse.

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