Thank you for using just answer.
How do you know this is a security issue?
What exactly is the car doing?
ok, so this light is to the LEFT of the steering wheel then correct?
I need to be sure because I think this was an add on system not a factory alarm then.
This red light.....does it also act as a button that will toggle in and out when pressed on?
This is not a factory system then, this was a common system to be added by dealers.
Do you have a remote for the system that still works?
Most likely your battery went low or weak and caused this alarm to reactivate.
Here is how you oficially disable it (until the battery is dead again):
Starting with the button pushed in I need you to push the button 3 times, then insert your key into the ignition and cycle it from full off mode to ON (not start) 3 times, when the key hits the ON mode for the 3rd time it is supposed to shut the system down and allow the truck to start. If this does not work then there is an issue in the control computer for this system and it will need to be removed or replaced. This is usually tucked up under the driver dash, if you follow the wiring from the indicator light it will lead you to the controller. Simply unplugging this will bypass the unit.
Read my entire post from above. If the sequence did not work then this is an issue in the controller and it will need to be disabled or replaced.