I recently had an after market radio installed on my 99 Deville and since then I have been having a daily issue with my factory security system. At least once a day now the car will not let me disarm the security system until the car is started and the alarm is going off. It is happening completely at random and the employees at the shop I had installed it are saying that it's not an issue with the radio or "interface" that they installed but I am suspicious since the problem never existed until I had the radio installed.
It looks like they installed a GMRC-03 interface if that makes a difference.

When the problem occurs I can sit there and hit the unlock button on my remote and hear the chime coming from the dash but none of the lights come on and none of the buttons on the remote work. The only way to get into the car is to use the door key and then the interior lights and all buttons in the interior still do not work.

Anybody got any ideas or heard of anything like this before?

 

Have radio shop re-install factory radio and see if problem goes away. If problem is still there, try to fix the problem before re-installing other radio.