Troubleshooting Alarm Trigger

Hi guys. I'm trying to troubleshoot an Omega AL-532atv alarm system in my 87 Ford van (all specs below). 2 doors currently will not trigger the alarm. It was originally professionally installed, but hasn't been working the last several months. I think the problem lies somewhere in 1 or 2 door switches. After pulling the brain and reviewing the schematic, it looks like the 2 front doors are connected to a positive trigger (Ford BLACK/ blue to Alarm Violet). Front doors are now working and triggering alarm.

There is one pin switch that was installed in the rear cargo door and another contact type switch in the sliding side door. The side door switch looks almost like 2 magnets that make contact together and it has 2 wires --one is grounded to the door frame. I've taped the 2 contacts together for testing at the moment and it remains grounded.

After tracing the wiring as best I can, the rear door pin switch looks connected to the alarm's GREEN (- input) wire. The side door switch seems to be spliced into the wire that runs from the GREEN input of the brain, to the rear pin switch. Although, I'm not certain it isn't tied to the VIOLET + trigger. Neither of these 2 switches are triggering the alarm. I don't see diodes anywhere, but both doors were previously working the way it's currently wired. So, can anyone offer some advice on how to troubleshoot these 2 switches w/o re-wiring everything? And can/could these 2 doors be tied together off the GREEN input w/o using diodes?

Thanks in advance for any input and Great site!

-Omega AL-532atv Alarm (Omega sent diagram for K-9 Five ATV)
-87 Ford Econoline van
-new remote battery
-reprogrammed remote (it wasn't activating alarm)
-tested GREEN input by grounding an unmounted pin switch and connecting it to the Green input -- triggered alarm
-Replaced rear pin switch
-All fuses are fine
-Got wiring diagram from Omega in PDF format


Alarm Inputs      Ford Wiring Diagram:
violet: + trigger           Door Trigger: BLACK/ Blue (+)
blue: - instant            Domelight Supervision: Use Door
green: - trigger

Sounds like you have a magnetic reed switch on the sliding door. Generally a normally closed switch is used for applications like this. One wire is grounded, then once a magnet is brough in close proximity to the switch, it opens and the ground is no longer sent through the second wire.
     
      You said when you taped the magnet to the switch you still saw a ground through the wire connected to the alarm (if I'm reading correctly). This will cause the alarm to think that the door is always open and thus bypass the door trigger during it's arming sequence. Sounds like you need a new reed switch on the sliding door.

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Life moves pretty fast; if you don't stop and look around once in a while; you could miss it.

Thanks for the response. I'll have to find a multimeter tomorrow.

Actually, I didn't check for a ground on the switch, I just left the grounded wire in tact and taped the 2 contacts pieces together. I'm assuming taping them would let the alarm think the door is closed so I could check the other pin switch.

So is this reed switch a Negative trigger switch and can it still be tied in with the pin switch?

Yes the reed switch provides a negative trigger, but the pin switch will be a negative trigger too; it just uses the mounting point of the switch itself as a ground.  When the switch is depressed, the connection is opened.

Another option would be to disconnect the alarm trigger wire at the two switches, one at a time, and see if the problem continues; the problem should disappear with the faulty switch disconnected.

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Life moves pretty fast; if you don't stop and look around once in a while; you could miss it.

Thanks for the help Mr Hockey. I ended up replacing the reed switch with a pin switch and all is working.