Brake light , turn signals, and flashers not working

We need to go back to the lights and check what the voltage is on the brown wire at both lights. Safe assumption that you will not have voltage. If it is 0 volts then we most likely have a wiring issue going to the lamps on the brown wire. As you can see from the wiring diagram this wire is spliced 3 times from the switch to the lamps. More then likely you have an issue at one of these connectors.

However, if you have very little voltage, then we have high resistance in the wiring or a loose ground for these lights.

Let's start with checking for voltage and go from there. If it not 12 volts when these light should be on, then we need to go backwards in the system following that wire until we find where we have 12 volts.

Let me know what you find and we can go from there. Thanks