alarming my fuel door

Just wondering since I don't have a locking fuel door, if I could hook my alarm up to it, to make my alarm go off if someone opens it? Alarm is a Viper 791.

Use a magnetic reed switch for this application.Jeff

Velocity Custom Home Theater

Mobile Audio/Video Specialist

Morden, Manitoba CANADA

I am not familiar with your particular alarm, but I am sure that there is a hood/trunk wire. Maybe someone else can tell you what color the wire is.  As stated above the best way to do this is with a magnetic reed switch.  Radio shack sells one but it is a little large.  There are 3 connections on the switch.  Common, Normally open, and normally closed.  You need to ground the common connection, and connect the normally closed contact to the wire from your alarm.  You will need to mount the magnet to the fuel door and mount the switch to the stationary part of the car, in a position so that when the door is closed the magnet is close enough to the switch to make the connection open.

I have a extra door trigger wire I could use. I used the +, but have the - available. So would I just run this wire to my fuel door, and go to radioshack and get a magnetic reed switch?

using a relay convert the polarity to pos and then diode isolate the wires from hatchpin/doorpin with the reed switch.

Does your alarm have a - trigger hood/trunk pinswitch wire?

You can use the negative door trigger input if it is unused. Depending on your alarm and how you have it hooked up, you may wish to hook it up to another trigger point. If you have separate triggers for different zones (hood, trunk, doors etc) your alarm will notify you if it has been triggered and what zone was violated. Having everything on its own zone gives you a better idea of what happened to trigger the alarm. This can be useful if you also have false alarms. When buying a magnetic reed switch, buy a good one. Cheap ones are prone to problems. The magnet and switch must be close together and where you intend to mount them, this could present a problem. Check out the mounting location first to see what you have to work with. Spray the contacts on the switch to prevent corrossion after installion.sparky

Well from my alarm I have a -gray hoodpin wire. I used this already.I also have a -blue trunk trigger-used. +violet door trigger-used. I have free a -green door trigger wire. So I guess I just run the -green door trigger to the fuel door and hook it up to the magnetic reed switch. How would I set up the switch? I've never even seen one before. Thanks alot

The alarm is a viper 5900 alarm/r.s./keyless entry, with 2 way pager lcd.

I guess you could use the unused positive door trigger wire.  You will have to run a positive wire to the reed switch. Just seems easier to use either the hood or trunk wire.  You can have 2 sensors on one wire.  You will need to decide which zone you want to have duplicated when your remote receives an alarm.  It will have to give you a door violation or a hood or trunk when the fuel door is opened.   Either of the 3 choices will work fine.