What does the brake light, horn and indicators have in common?
Check the orange green wire (position 9 on the ignition switch harness) There should also be a black/blue wire in that same spot, that one goes to the horn.
They both are fed by the orange wire to the fusebox (fuse 4)
So, if there is power in the orange, follow the green/orange wire.
If there is no power in the orange, check the fuse and the wire to the fusebox.
My guess would be that this connector just slipped off when you plugged the new harness.