If I'm understanding your description of your voltage tests at the fuses, your brake light fuse is blown.

Fuses should have the same voltage on both ends, they aren't switches or loads.

Change some fuses. I bet you shorted the brake light wires while fooling around under the dash.

Also, don't the 4 ways get power through that same fuse?

Edit. Just saw your test with the jumper wire, you have confirmed a bad fuse. Basically you made your brake lights a test light.