2001 GMC Jimmy brake lights on dash

Brakes problem
2001 GMC Jimmy 6 cyl Two Wheel Drive Automatic 55k miles

My 2001 Jimmy's red and amber brake light and abs come on after starting engine 2nd time and will usually come on rest of day and stay on. Only after letting it sit for usually overnight will it start without the lights on dash but second start of day they come on again. Tried checking for loose electrical connections on abs pump and abs computer ok. Perhaps wheel sensors? If so how are they checked out and or replaced?
Thanks