SRS light on

Well it may be a coincidence but the first thing I would do is be sure that you did not accidentally unplug one of the connections while replacing the headlight. If you do not see anything or are sure you did not then the next step would be to scan the system and pull the code(s) that have turned the light on (and disabled the SRS system). The code will give you a better idea of where to look and what to look for.