This concerns a 2004 Blazer....Truck starts up, all the warning lights go off (including security) runs fine. The ignition switch was replaced about 2 years ago, haven't had a problem starting. All is well except for a new problem the security light now stays on, (doesn't flash) when I turn off the ignition. This wouldn't bother me, except it is causing a draw on the battery when it sits for a day or so. Recharged the battery...starts right up...runs fine ..... except the security light will not go off after turning off the ignition. My temp fix is to just disconnect one of the battery terminals when I park it. It does have an aftermarket lock-unlock with fob installed by previous owner, which also works fine. Any suggestions? Thanks in advance

 

I have a 1999 Service manual so this might not exactly apply but I think generally it might.

According to the manual, one reason the SECURITY light will stay on continuously is if the IPC (instrument panel cluster) is unable to communicate with the BCM (body control module).

After this, there are a bunch of tests to go through which starts with reading the DTCs (diagnostic trouble codes). The more sophisticated readers can read these.

Sorry I don't have any more for you.