I was going to do a How-to on a DIY blinking third brake light that uses an old school flash module from Autozone. It's nothing new but a few people ask me about what parts to buy and how to wire it. In a nutshell, you just cut the positive (+) wire going to the third brake light bulb and insert this into the circuit. Cheap, simple and uses the stock bulb. Drawback? It is slow and mechanical.
Recently, solid state flash modules have entered the market that supercede the old tick-tock flasher mod but most of them require the purchase of an LED bulb to function.
This next evolution takes it a step further in simplicity, parts and cost. It's just a flashing, direct-replacement LED bulb. This one is a 3 watt SMD mounted in a 320-degree mount so it's much much brighter and noticeable than a standard incandescent bulb and should last much longer. Because it is only a third brake light, there is not need for a load balancer such as needed when replacing turn signal bulbs with LED.
No need for a complicated DIY about wiring nor the cost of a flash module or wiring. Just buy this:
*The Miata uses a 1156 bulb for the third brake light