2004 Monte SS 3.8SC.I know this has been a common topic but here's a different question. Overnight my car is dead, resting voltage after charging it is good on the new battery and alt is new. Solus scanner shows everything off or inactive with the exception of the ambient light sensor shows 2.4 volts in sunlight and 4.6 in dark with car off and after sitting for about 30 min. Is it going to show voltage while car is off? Also on cool mornings the windshield condensation has a clear spot right over the defrost vent. Did a parasitic draw test and found no changes, Pulled radio fuse, even BCM right out and still dies. Any ideas?

 

Good detective work.

Since the ambient light sensor lives on top of the dash (the little red bulb protruding through the top of the dash next to the defrost vent), I think you're on to something. The clear spot on the windshield could be a sign that the sensor is putting out heat from a short. However, problem with the ALS should throw a code. The next question would be...is there a problem with the DRL circuit. Check to see if there is any, even the dimmest glow from the headlights.
Here's a video on the ALS:

 

circuit at als checks fine at 4.5 ohm and 4.9 volts but will not shut down at all even after car sits for an hour or overnight still have readings on the scanner of 2.4 volts or more depending on brightness. As I stated before I took the BCM completely out overnight and it still dies. I'm at a loss on this one.

 

Ok so apparently my meter was junk so I got another and tested for draw. Let vehicle set for an hour and started pulling fuses. Start draw was 3.7amps and after pulling radio fuse dropped to 1.3 and the BCM/cluster fuse along with radio fuse out dropped it to a 0.4. So is my BCM and radio shot?