brakes are designed to squeak when the get low. the last few mm of friction material are different to the rest. they countain a slightly different compound that is designed to scream like hell to let you know that the pads are low. because they a single side slider caliper you need to take the wheel off if necessary to take a proper look at the pads on both sides of the caliper, as the inside one may have worn much further than the outside pad.
failing that if they are health good pads and squeaking its because someone has either not put the vibration plates in, some pads have them, others dont. if you don't have any fair enough but you need to properly coat the back of the break pads with copper grease to stop them from singing.
as for the light thing, can't help you am afraid.