Since the turn signals and hazards work -- this means the grounds, wires and bulbs are good because the same two circuits (wires) are used for brake lights unless it's cobbled-up in some way.

I assume you have the solid-state flasher since you have hazards – correct?

Do you have a three-lever switch?

If it is wired like the M715 with a three-lever switch, we can determine if the problem is in the signal coming to the column switch by doing the following.

Disconnect the connecter from the switch on the column

If you have a three lever switch --place it in Service Drive.

You should have power at pin G of the connecter at the switch on the column. I suspect you do since the turns and hazard work

Step on the brake and see if you have power at pin D of the connecter at the switch on the column.

If there IS power at pin D with the brake pressed – the problem is in the turn switch.

If pin D is DEAD with the brake pressed, then there are two possibilities where the problem might be. 1) the three lever switch or 2) the brake light switch

We can go from here.