https://www.amainhobbies.com/vaterra...xoCVTgQAvD_BwE

Guessing your getting something like this. The controller that it comes with will have all the flashing functionality. To turn it off and on you can use something like this.

https://hobbyking.com/en_us/turnigy-...E&gclsrc=aw.ds

Or this

https://www.ebay.com/itm/Two-Way-Cha....c100677.m4598

If your doing something more custom then items like this might down as well.
HobbyPartz Flash LED Light Kit for RC Cars