2004 SS, 163k miles

My standard procedure when I get into the garage at night is to pop the trunk, get my stuff out, then leave the trunk open until the next morning when I put my stuff back in. The light always turns off after 5 minutes or whatever, right? Well, not anymore. If my trunk is open, that light is on. I had a dead battery the other morning then when I fixed it later and started searching around I settled on the trunk light.

Any ideas "where" the timer is or why it would suddenly stop working?

 

Sounds like the switch is stuck. You might be able to clean the button that's like a door light switch button.
Here's an old thread: https://montecarloforum.com/forum/ge...k-light-41528/

If that switch has a delay ("timer") it might be controlled by the "retained accessory power" system and the BCM, and if that is the case and there was a fault all the other lights that turn off after removing the key and closing the door they would stay on too.

I just tested this on my '00 SS and it took about 15 minutes for the trunk light to go out when I left the lid open, much longer than the dome light etc. after doors closed. I also checked the schematic for Retained Accessory Power and the trunk light is not shown to be on the circuit, so the "timer" must somehow be incorporated into the switch. The bulb is very low watts (maybe 5W), but if the battery is weak it could be just enough to pull the battery down. I suggest you double check to see if the light goes out within 15 minutes. If it does, you might want to replace the battery. You could also replace the bulb with an LED one that draws less than 1 watt.