Hi to you all.
Well, the first problem in the schematic that you made is using a linear voltage regulator (LM7805) and the second problem is using incorrectly the LM7805... like TomGeorge, cbaker391 and Grumpy_Mike were saying, you forget the caps from the input and the output of the regulator to stop the oscillations. (don't worry, everybody learns from mistakes...)
The linear voltage regulator weren't design to be used in this way, they are slow, they oscillate and they are extremely inefficient and you will need a decent heat sink for cooling it... you can make them work in this way, but it will be a mess.
In my first clip i just shared an idea and i didn't talk about triggering the input and powering the project, so in my second version i explain how simple is to use optocoupler to trigger the input and in the third version i showed how you can use a step down buck converter to power everything up (see attachment).
Modern turn signal lights v2.0Modern turn signal lights v3.0A good and cheap step down buck converter is MP1584EN, i've been using it in countless projects and in never failed for almost two years (yet).
Hope this info helps you and others that are trying to recreate my or other projects.
For other versions check out my channel
Think small, build big!