I looked into the tail light harness that you said you had installed on your 1995 Pontiac Bonneville and since it draws the power from the tail light circuits I believe that is why your tail lights are hyper-flashing.
What I think would fix the problem would be to install a powered unit that draws amperage from the vehicle battery and only uses the tail light circuits as signal wires. For that I would recommend you get a Curt Wiring Kit # C59496. I attached installation instructions and... view full answer...