Why does my brake warning light stay on, on my 2000 ford expedition ?

i have a 2000 ford expedition xlt (not 4wheel drive) i took it in for an oil change and the guy there told me that my brake pads needed to be changed and that i also needed a ball joint replacement and coil pack. so i got everything done today including an unexpected brake caliper replacement. and now all of a sudden while driving, my brake warning light wont turn off. ive never had this problem before. im assuming it has something to do with how the guy put my break pads in but i know nothing about cars. please help. is this something i should be worried about ? what could be causing this ?Why does my brake warning light stay on, on my 2000 ford expedition ?Since you say that the light came on after replacing the brake caliper, it may just be that the brake fluid level in the master cylinder is low and turning the light on.Why does my brake warning light stay on, on my 2000 ford expedition ?Take it back to that shop. I believe there's a disc wear sensor on the front brakes. It wasn't installed properly.