alarming my fuel door
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=102208
Printed Date: May 14, 2025 at 5:57 PM
Topic: alarming my fuel door
Posted By: 12voltexpert
Subject: alarming my fuel door
Date Posted: February 14, 2008 at 8:22 PM
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.
Replies:
Posted By: Velocity Motors
Date Posted: February 14, 2008 at 8:48 PM
Use a magnetic reed switch for this application.
-------------
Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: i am an idiot
Date Posted: February 14, 2008 at 10:02 PM
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.
Posted By: 12voltexpert
Date Posted: February 16, 2008 at 10:15 PM
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?
Posted By: tedmond
Date Posted: February 16, 2008 at 10:40 PM
using a relay convert the polarity to pos and then diode isolate the wires from hatchpin/doorpin with the reed switch.
Posted By: i am an idiot
Date Posted: February 17, 2008 at 3:59 AM
Does your alarm have a - trigger hood/trunk pinswitch wire?
Posted By: sparkie
Date Posted: February 17, 2008 at 11:08 AM
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
Posted By: 12voltexpert
Date Posted: February 20, 2008 at 9:54 PM
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
Posted By: 12voltexpert
Date Posted: February 20, 2008 at 9:57 PM
The alarm is a viper 5900 alarm/r.s./keyless entry, with 2 way pager lcd.
Posted By: i am an idiot
Date Posted: February 21, 2008 at 6:04 AM
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.
Posted By: sparkie
Date Posted: February 22, 2008 at 12:38 PM
You can use the green (negative trigger) door circuit trigger. Run it to one of the two contacts on the reed switch. It should be to the normally open terminal, but check your switch with a ohm meter first. The NO (normally open)terminal should have continuity with the other contact until you place the magnet that comes with the switch next to it. Some swithes you may have to connct the green wire to the NC (normally closed) terminal. The CO or common terminal on the switch goes to a good ground. The idea is that if the magent is mounted to the fuel door and the switch to the body, when you open the fuel door the magnet is moved away from the switch. The switch then connects the two terminals and sends a ground to the green door trigger circuit. Make sure that you mount the magent close to the switch so they work as desired. Different magnetic reed switches have different tolerances. Some will activate when the magnet is only a fraction of a inch away from the switch, while others allow an inch or so of movement before responding. Remember to protect the contacts on the switch in some manner to prevent corrossion.
-------------
sparky
Posted By: i am an idiot
Date Posted: February 22, 2008 at 3:35 PM
He needs to use the normally closed contact. With the magnet near the switch it will make the contact open. Open the door and the magnet leaves allowing the switch to close.
Posted By: 12voltexpert
Date Posted: February 22, 2008 at 6:22 PM
Could I use an extra hood pin in the fuel door. So when it opens the alarm goes off, same as the hood pin under the hood. I think it would work better than the magnetic reed switch which can false. What do you guys think.
Posted By: gregbbb
Date Posted: March 08, 2008 at 10:26 AM
Hi I am in the boat as you just wanted to know if you used the extra hood pin for your gas door? and if it works. I have the same viper as you but i have the trunk - wire free or i dont know if can use the same green ground wire that go's to my bypass? Did you ever get it to work? Thanks
Posted By: andrewdirt101
Date Posted: June 18, 2008 at 4:31 PM
I see this is an old thread... but I have the same question as originally posted. Where can I find a magnetic reed switch suitable for this? I've wired a set of horns directly from the battery, with a toggle switch in the cab of my truck to switch the system off or on. When switched on, the power will be blocked by the switch at the fuel door, and when opened, the circuit completes, and power is fed to the horn relay, which in turn feeds the horns. Of course, if I don't want an ear-full at the pump, i just push the toggle to "off" and then i'm free to open it without any racket. i just need a reed switch that can handle the current flow. anybody have any suggestions?
Posted By: i am an idiot
Date Posted: June 19, 2008 at 7:12 AM
https://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&productid=2419298&accessories=accessories&kw=magnetic+switch&techSpecs=techSpecs¤tTab=techSpecs&custRatings=custRatings&sr=1&features=features&origkw=magnetic+switch&support=support&tab=summary Above is a switch that should work for you. The only problem I see is that I am not able to find any specs of the current capacity of the switch. A standard Bosch/Tyco relay has a 75 ohm coil, thus making it pull 160 milliamps to keep it energized. Using this switch the way the other guy was using it would be no problem. He was connecting it to an alarm. The following link is to a relay that pulls only 30 milliamps. The switch is going to be able to handle this current. I have no idea how much current your horns pull, but if it is close to the 10 amp max of this relay, you may have to make this relay trip the bosch/tyco relay and let it handle the current. https://www.radioshack.com/product/index.jsp?productid=2062482&cp=&sr=1&origkw=relay&kw=relay&parentPage=search
Posted By: andrewdirt101
Date Posted: June 20, 2008 at 12:30 AM
i see what you're saying. i found that switch last night and wondered the same thing. i'm sure the horn relay i've got pulls around 160 mA as you stated. horns take quite a bit. 2nd only to the starter. so let me see if i got you right. i run wire from the switch to the 10A relay, and then from that relay, connect it to the horn relay. so id essentially be using one relay to feed the other. correct?
Posted By: i am an idiot
Date Posted: June 20, 2008 at 2:45 AM
Correct. If when you purchase the switch, there is a spec sheet with it, maybe they have the current capacity of the switch. If it is capable of 500Milliamps, you can go agead and run your relay directly.
Posted By: audioinstaller3
Date Posted: June 22, 2008 at 7:07 PM
That sounds like a good idea, with gas prices going up, and I'm sure people will be trying to cypher gas out of peoples tanks soon if not already. I would try and use a magnetic reed switch.
Posted By: lostissues
Date Posted: June 22, 2008 at 8:00 PM
this is directed towards the beginning of the post where people were saying to use the unused -trigger wire (to the fuel door) in addition to the +trigger wire (already attached to car doors). I know someone who tried to use both - and + triggers and it freaked out his alarm. just make sure you can use both triggers without confusing the unit. Jonathan
|