When I was in undergrad getting my chemical engineering degree, I knew I didn't have a passion for it. I liked it, sure, but I knew I would eventually want more out of my career. So I pursued business. I got my ChemE degree, minored in business, and then got an MBA. Since then I have been working as a process engineer for six years.
Even though I didn't have a passion for engineering while in school, I actually have really loved my job. I know that ChemE is very different than EE; the actual work has little to do with what you do in school. With EE, ME, and Civil, the work is more aligned with the design-type academic curriculum.
I didn't become interested in law until about a year ago. The more I looked into it and talked to attorneys about their work, I really started to like it. Even outside of technical law, like intellectual property, there is a lot of logic involved that an engineering mindset is geared towards. My interests are mainly in property and corporate/business civil litigation. Pursuing law is mainly because it greatly interests me, and to a very small degree out of boredom with my job and the lack of career future outside of engineering or potentially engineering management.
My advice is to not do law for the money. I'm not at all; I often forget that there is a real possibility that I will make a lot more money than I do now or ever will as an engineer. As for having a passion, I'd say that you may develop the passion in your job as I did. If you really, really want to pursue law because you love it, go ahead and do it. If you are unsure, then get a job as an engineer and set a plan to go to law school in a few years. Live cheaply and bank as much cash as possible. Keep in mind, however, that going back to school is tough. You get comfortable with the lifestyle of having income; you might not want to give up the possibility of having a nice car, nice house, and nice things. That's why I recommend saving and not spending. Additionally, with a car payment, house, maybe even a spouse and children, you might get yourself in a situation where it's near impossible to go back to school for family or financial reasons.
The best thing you can do, in my opinion, is to work as an engineer for a couple years, but plan on law school. You can always change the plan later. The work experience will be helpful in your career, and it will give you time to figure out what you really want to do.