1999 Blazer 4X4 all 3 brake lights are staying on anyone have this same problem thought it mignt be the CHMSL Relay but my model its not used
can try stoplight switch or multi function switch? any help will be great
thank you all

 

Sounds like the stoplight switch on the brake pedal assembly or a short in the wiring. The CHMSL is triggered by the stoplight switch. Disconnect the stoplight switch and test for power on both the orange & white wires. There should be +12V to the orange wire, but the white wire should not. If there is +12V on the white wire, there is a short in the system somewhere. While the stoplight switch is disconnected, test for continuity. It should close when the pedal is depressed, but open when not depressed.

It is possible for the multifunction switch to back feed into the stoplight circuit if things were to go really wrong inside.

 

Thank you for your reply I will check
hope its the switch