New guy here, just bought a 2000 SSEi and the lights come on automaticly during the day, sometimes. They will usually go out after I've been on the road for a while, but no consistancy to how quick they will go out if they ever go out. I'm sure it'* the twilight sentinal since I took it out and beat it on the dash and it went to working for about a day. So, where do you find one of these without going to the dealer? Advance auto didn't have it, or at least they didn't know what they were looking for.

They are listed here https://www.1stpontiacparts.com/partscat.html

sentinel sensor, bonneville, lesabre, w/o aux ac control
00-05 $27.33 $18.70
Electrical - Chassis electrical - Headlamps - Sentinel sensor sentinel sensor, bonneville, lesabre, w/aux ac control
00-05 $32.54 $22.25
Electrical - Chassis electrical - Headlamps - Sentinel sensor