Brake lights flashing

[tattooboy37]

Brake lights started flashing recently after no changes or recent work. I had installed a new turn signal mechanism some months back and had everything working nicely. I don't drive her that often and the last time I hooked up the battery and turned on key the brake lights started flashing. The funny thing is, I normally never had any flashers or switch for them either. They blink when the turn lever is in straight position. They both blink when I put on right signal and everything is normal for the left signal. front signals both work normal and do not flash. I did replace the battery lately too, don't see how that could affect things but I'm no electrical expert.
1963 C20