I have a Kahtec Smart Stop brake light (Delay Version) module installed on my 3rd brake light almost a year ago. It blinks 3 times before it turns solid. It would only do that after you press the brakes after 10 seconds. So if you are in stop and go traffic and presses the brake light within 10 sec frame, it remains solid. The module is small taped (double sided) at the housing of the 3rd brake light.
Here is a link upon installation on my 86
https://www.youtube.com/watch?v=RqNfHx3A-r4
Here is where I bought it showing different variants
Blinking Smart Stop - Flashing Brake Light