Why would a 2000 Blazer have no brake lights if the bulbs and fuses have been replaced?

Possibly the brake light switch. not sure where it is located tho. maybe under the dash attached to the brake pedal lever. it may have a spring loaded button on it so that as soon as you push the brake lever the least bit the button comes out allowing the switch inside to connect. this switch malfunction usually causes the brake lights to stay ON tho.hope this is the problem.

Have you considered the relay? I believe the brake lights are engaged via relay on the 2000 Blazer. Check your hazard lights and your third brake light.

I am the previous anonymous. I have done some research and discovered that your vehicle has actually been recalled because of this very problem! Check the NHTSA's website or contact your local Chevrolet service center to set up an appointment for free service on the recalled part (actually a multifunction switch which also relates to your hazard lamps). The recall Campaign ID is 01V364000. The Part Number is 506377. .

check your hazard switch. despite what most dealerships say, you can replace just the hazard/4-way switch which is much, much cheaper than the entire turn signal assembly they try to sell you. that fixed my brake light problem

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brake lights are wired through the turn signal switch. the switch is needed to interrupt power to the brake light that needs to blink for turn signal useage., also to allow the lights to blink when flashers are used.

turn signal switch failure is usually the cause of no brake lights. replace the switch assembly. if the third brake light always works then it is the turn sig switch assembly that is causing the issue with the brake lights not working.