I own a 2008 Cobalt LS 2.2L Sedan, and the upper rear tail lights blew out. I replaced the two dead ones (912 bulbs) with 921 bulbs that came inside some sedan tail lights I bought off a junkyard Cobalt. (They were reverse bulbs.) The bulbs worked fine, is it safe to use these? I haven't driven the car yet after changing them.

 

should be fine.

 

it may have issues over time but presumably the junk yard bulbs will die quicker than a new bulb so you should be fine. I personally would say look into LED bulbs