On my 99 Yukon slt, non of the 3 brake lights turn on, checked the bulbs and they are good, same with the fuses, what should I check next?
Brake light switch on the brake pedal would be what I would check next. Could be out of adjustment or faulty. Some have a small rubber plug that the plunger rides on in the pedal. These tend to come loose sometimes not allowing the switch to be activated properly.
1999 GMc Yukon Brake light switch. Never saw one looks like this but looked at three parts suppliers and here it is
But I agree with dandyoun. That's the next step. You remove a panel under the steering column to get more room. Pull the switch up from the brake pedal bracket till it comes out
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