Hey guys I got a 2000 mc ss 113000 miles with some weird intermittent electrical issues. First thing i notice is the driver side headlight goes out very rarely happened twice so far. Window didnt respond twice but this was only one occurrence. Seatbelt light went on twice whie i was already strapped in. The more frequent problem is seeing the security light when key is on but its starts fine untill yesterday it would crank but not stay started and died, couple cranks later started fine.
Also sometimes when the ebrake is applied the lights stay on, from what i see the headlights are supposed to stay off untill the ebrake is released.

Fuses are good . Checked connections under dash and hood, all good

Sidenotes: I noticed a pretty significant drop in voltage and rpm when i roll down the windows also lights dim(more on the driver side than passenger). Could be alternator/voltage reg?