adding sensor to oem ford alarm

I want to add a glass break sensor to my oem alarm on a 2002 ford explorer.

I want to utilize the oem door pin circuit so that the glass break sensor will create an alarm condition just like if the door had been opened. I presume this would be the easiest or only way to connect an additional sensor.

I havent really read much about people adding to oem systems (although i have seached), but the oem alarm is all i need once i add the glass break sensor. 

Basically I want the glass sensor to feed the door pin and make it as if a door was opened (when it senses glass break), thereby triggering the alarm, and I know it can be done, and ,may require a relay or diodes, I just dont know what or how to make it work.

I have found a sensor I would like to use, but it is a "negative trigger input", and I need help connecting this to the existing door pin system.

I truly appreciate any input or help, this is my first post here, and i will be proud to redistribute this info to many who would also like this additional protection, without having to buy an aftermarket alarm.

The procedure is pretty basic - locate your OEM alarm trigger:

|     DOOR TRIGGER|BLACK/ lt. blue      |+ |driver kick panel           |

and connect the sensor output to this wire.  You should isolate the OEM door pin from the sensor output, and in your case you will have to, because you will also need to convert the polarity.

If you can, find the specs for the output of the glass break sensor - if it is at least 100mA you can drive a standard automotive relay with it.  If it is less then 100mA you will need to get a reed relay (or some other type of switching device that doesn't require a lot of current).

Assuming it has a decent output, connect the (-) output of the glass break sensor to Pin 86 of a Bosch style relay.  Connect Pin 85 and Pin 30 to constant power.  Connect Pin 87 to the wire listed above.

For your glass break sensor you will have a few options, I would most likely connect the 12vdc wire directly to 12vdc, connect the ground to an ignition wire, and connect the output as listed above.  When the ignition is off it will rest at ground and provide ground to the sensor. 

One thing I would also look in to is if you truck has an OEM hood pin that triggers the alarm.  If it does, it may be a better signal to tap in to, as it won't cause your dome light to come on when it triggers!

What a fantastic and prompt answer!  I may have a few q's about the details here, but you have given me a great start!

First i will get specs on the output of the sensor, and try to find one with sufficient amperage.

"You should isolate the OEM door pin from the sensor output, and in your case you will have to, because you will also need to convert the polarity."

could you explain this part a little for me? How do I isolate the door pin from the sensor output, and how do i convert the polarity?

I assume that the negative trigger needs to be converted to positive trigger? How do I do that?

Many many thanks!

OK, I understand everything thus far, but I have two more questions...

Ive decided to use the hood pin as you suggested, so my dome lights dont blink while I drive.

However, i need to know which wire on the hood switch to use when wiring the relay as you suggested, and Is there a better spot to access that wire from the interior? (I have no wiring diagram)

Also, the sensor in question is a directed 506t, and I cant find any specs on it. Is the amperage output sufficient to use a bosch relay?

You did that too, didn't you?  Mine was a first gen 300ZX.  I just thought I was through for the day, then I got the phone call, if it would have been the dome light, he could have turned it off, it was the passenger door light. 

Believe it or not I've never hooked up a sensor this way, but I've read a lot about it in the G35 / 350Z world - it's a very popular mod (adding a shock sensor to OEM alarm).  The issue the G35 people were having is everytime the shock sensor was tripped the window would dip down 30mm then go back up - not the best integration!  I, myself, have been waiting for someone to come up with a module to hook a dual stage shock sensor up to an OEM alarm - that would be cool!

Finding the OEM hood pin wire may be difficult to do - you will just have to trace it.

The light won't actually come on while you are driving because it will be grounded to the ignition wire - therefore when the car is on the glass break sensor won't actually have power (it will have 12vdc on the power wire and 12vdc on the ground wire).