When first pushing down on the brake pedal, the dummy light (for the brake bulb(s)) lights up in the instrument cluster.

As quickly as it appears, it again disappears.

I checked, and replaced-even though both were good, both brake light bulbs, as well as ensuring the third light was in full working order.

I cleaned the contacts (for the bulb holders), as well as replacing fuse #11 (on which the bulbs sit).

I also checked the wiring harness to both holders, as well as the harness to the third light, and they all look to be intact.

Any suggestions would be most appreciated.

Thanks, and I hope that your weekend is most brilliant!