yes there are but if you use a 12 volt on a 6 volt sys not muchof a difrants and no you would not need an aditional power sorce to use a 555 it is all a mater of wireing all you have in a car or truck is 2 power sorce and thay act as one. and no you can do it with a 555 and a zener. the aplication is simple the hardist part is the 555 pine lay out.