code alarm ca 100

The system should not arm if the door is open and the vehicle is set for passive arming. Arming should start after the door is closed.   I assume you hooked up the dome light signal (and it is working) to detect if any door was opened.   (Yellow negative active wire in the dirver's kick).  Are you certain the dome light works consistantly...no flakey door pins?  Do both doors cause the same issue?   I agree with Monty--It sounds like the doors are being ignored, and the system is arming, and the shock sensor is triggering when the door shuts. 

You may want to sit in the truck, arm the system, then open the driver's door to confirm the system sees the door and then triggers.  Then try the same with the passenger's door. 

For the issue you describe, I would use diagnostics from the CA100 to figure out what is triggering the system.

When this happens again, disarm the system.  You should get 4 chirps and the light will flash 3 times.

Enter the vehicle and before turning on the ignition switch, observe the LED flash pattern.--This should tell you what triggered the alarm.

From the CA100 owner's manual:

If the LED flashes 2 times...pause, 2 times...pause etc., then an intrusion attempt was made to open the hood, trunk, or by an accessory triggering device.

Check the vehicle for indications of forced entry to these openings.

If the LED flashes 3 times...pause, 3 times...pause etc., then an intrusion attempt was made to the vehicle doors.

Check all doors for indications of forced entry.

If the LED flashes 4 times...pause, 4 times...pause etc., then an intrusion attempt was made by impact or a strong vibration that the shock sensor

detected. Check the vehicle for possible damage to the glass or body panels.

If the LED flashes 5 times...pause, 5 times...pause etc., then an intrusion attempt was made by the ignition switch.

NOTE: The LED intrusion warning indications are stored in the system's

memory and will be erased when the ignition switch is turned on.