Applying to UC's, Interest for Major?

Applying to College
1

For UC schools is it important to show interest in the major that you are applying for?

I know major affects your admission to UC’s by quite a bit, so I was wondering if it was very important to demonstrate through EC’s or something like that your interest in the major.

For example: If a person wanted to become an engineer but had business-related EC’s, would it be bad for them? Something along those lines.

Thanks!