Brake lights do not come on when break pad is depressed.Is ita relay problem. on 1998 Volvo S90

Problem started after AAA installed a new battery. The marking indicators work but the brake light will not come on when depressing pedal. Is it a fuse issue, relay issue or a battery light switch that needs to be reeplaced. I have been reading around on blogs and nothing definitive. Want to know wear to start?

Asked by for the 1998 Volvo S90