brake light problem with 69 chevelle

I am troubled with an intermitent brake light issue. Some times my brake lights work fine. I take a corner and my left brake light stops working. I hit a couple of corners and a bump and my right one goes out and left is working. I have replaced the sockets for the bulbs. Grounded well and problem persists. Anyone have any idea what I should do next?
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Welcome to AF. You may want to consider the turn signal switch or the wiring going to it as the brake light signal goes thru it. Do the turn signals work when the brake lights don't? The brake lights and turn signal lights are both the same filiment on the rear light bulb.