Brake lights not working

Inside the head light switch is a circuit breaker that where you get the flickering, you have a short from the headlamp switch to the head lamp dimmer switch (the dimmer is high and low switch), Follow the wire leading to the dimmer switch there is a short in there

Sounds like there's a bad ground for the rear lights. One way to verify it is by turning on the left turn signal with the headlights off, then watch what happens on the rear. If you see the right side flashing too, remove the bulbs on the right and the left one will go off.

If you have replaced these parts, you need to trace the wires. Is the check engine light on? If so it may have store a "B" for body code, if not on could be a wire...

Might be damaged at trailer hitch area...