Re: Arduino/relay reliability question

Modifying a car, without much knowledge what exactly are the consequences of that modification, might kill more than one person. That is way worse than playing with AC voltage which may kill just you.

I think that you will not get much assistance here unless you show more knowledge and understanding about what you intend to do.

Ditto. Without meaning to be too harsh: You. Are. Nuts.

Putting your life in the hands of hobbyist-level hardware that has had no qualification on EMI susceptibility, voltage transients, etc. is just a terrible idea.