How can i disarm/turn off the security system?

This may be a bad rear integrated control module. or connection or wiring to it.
REAR INTEGRATION MODULE (RIM)
The CTD system is an internal function of the rear integration module (RIM) which utilizes class 2 serial data and various switch input information to perform CTD functions. When the RIM detects an unauthorized entry, the RIM sends a message via the serial data circuit to the DIM to activate the horns and exterior lamps. The RIM has 5 basic modes. Disarmed, standby, delayed, armed, and alarm for operating the CTD system. The 5 modes transition from one step to the next in the following order:

When in the disarmed mode, ignition is OFF and any door is open the RIM commands the instrument cluster to flash the SECURITY indicator via the class 2 serial data circuit. The RIM has the CTD system in a disarmed mode until the following conditions are detected:

Ignition key turned to the OFF position
Any door open
Doors locked by either the power door lock switch or the LOCK button on the keyless entry transmitter

The RIM enters the standby mode when the above conditions are detected. In standby mode the RIM commands the instrument cluster to illuminate the SECURITY indicator via the class 2 serial data circuit. If all the doors are closed and the LOCK button on the keyless entry transmitter is used, the RIM enters the delayed mode.
When the last door is closed, the RIM enters the delayed mode for 30 seconds . In delayed mode the RIM commands the instrument cluster to illuminate the SECURITY indicator on steady via the class 2 serial data circuit.
After 30 seconds , the RIM enters the armed mode. In armed mode the RIM commands the instrument cluster to turn off the SECURITY indicator via the class 2 serial data circuit. Any forced entry activates the alarm mode.

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Do you have a dimmer for interior lamps? Like a rheostat, a little wheel that you turn up or down to brighten or dim interior lamps. Usually the instrument cluster lamps brighten and dim the same way.
Can you brighten and dim the other interior lamps?

Here's some info as it sound like the theft deterrent is armed.

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Reset Procedure

NOTE: This information applies to a Vehicle Theft Security System (VTSS) that was armed when the battery was disconnected and reconnected.

When the armed VTSS senses that the battery has been disconnected and reconnected, it enters its power-up mode. In the power-up mode the alarm system remains armed following a battery failure or disconnect. If the VTSS was armed prior to a battery disconnect or failure, the system will have to be actively or passively disarmed following a battery reconnection.

The power-up mode will also apply if the battery goes dead while the system is armed and battery jump-starting is attempted. The engine no-run feature will prevent the engine from starting until the alarm system has been actively or passively disarmed.

Passive disarming of the Vehicle Theft Security System (VTSS) occurs when the vehicle is unlocked using the key to unlock either front door or the liftgate. Active disarming of the VTSS occurs when the vehicle is unlocked by depressing the Unlock button of the Remote Keyless Entry (RKE) transmitter.

Once the alarm has been activated (horn sounding, lights flashing, and the engine no-run feature), either disarming method will deactivate the alarm.

Depressing the Panic button (if equipped) on the RKE transmitter will also disarm the VTSS, but the horn will sound and the lights will flash for about three minutes as part of the Panic feature. The horn and lights can be stopped by pressing any of the RKE transmitter's buttons or driving the vehicle above 15 mph.

Probably a bad Body Control Module. Find out which switch (which door switch [LF door, LR door, RF door or RR door switch]) causes that to happen to help narrow down a wiring issue.

There is a wire from the drivers door lock to the security system. Try unlocking the driver's door with your key to see if this will disarm the system.

throttle positioning sensor or egr

do you have any kind of entertainment systems hooked up to the battery for instance the subwoofers in my car constantly make my lights dim and brighten if i have them loud enough

Alarm Module Reset Procedure
NOTE: This information applies to a Vehicle Theft Security System (VTSS) that was armed when the battery was disconnected and reconnected.
When the armed VTSS senses that the battery has been disconnected and reconnected, it enters its power-up mode. In the power-up mode the alarm system remains armed following a battery failure or disconnect. If the VTSS was armed prior to a battery disconnect or failure, the system will have to be actively or passively disarmed following a battery reconnection.
The power-up mode will also apply if the battery goes dead while the system is armed and battery jump-starting is attempted. The engine no-run feature will prevent the engine from starting until the alarm system has been actively or passively disarmed.
Passive disarming of the Vehicle Theft Security System (VTSS) occurs when the vehicle is unlocked using the key to unlock either front door or the lift gate. Active disarming of the VTSS occurs when the vehicle is unlocked by depressing the Unlock button of the Remote Keyless Entry (RKE) transmitter.
Once the alarm has been activated (horn sounding, lights flashing, and the engine no-run feature), either disarming method will deactivate the alarm.
Depressing the Panic button (if equipped) on the RKE transmitter will also disarm the VTSS, but the horn will sound and the lights will flash for about three minutes as part of the Panic feature. The horn and lights can be stopped by pressing any of the RKE transmitter's buttons or driving the vehicle above 15 mph.

Have your charging system checked. I had a similar problem with a chrysler van - the lights would brighten and then dim periodically. it turned out to be the battery.

2000 chevy venture run good but my lights flickers and have to jump. After I jump the van and put my meeter on the battery its reading 14.volts at idle. I can drive around to store cut the van off come out it starts fine leave it overnite and it don't started.