I bought a 6 LED Peterson light that works the same way from a local auto supply. Flash twice, off - flash twice, off.It cost about $60 but has the modulation built right into the circuitry.
Ran two wires up into the rear storage compartment (if you can call it that!!!) and spliced into one of the brake light circuits - hot and ground. didn't cut any wires - just used the quick connects.
The neat trick about this one is that there's an external mount that you can get that fits almost perfectly where the reflector mounts down below the license plate. Looks really good and is very bright...
Check it out here:
https://www.pmlights.com/products.cfm?cId=1...59&pId=2312