Can I do BA with psychology after dropping 2nd yr Diploma in engineering?

It's understandable that you may be considering a change in your field of study, especially as a 2nd-year student. To determine if psychology is the right fit for you, first, you should do some research and gain a better understanding of the field. While many people consider this field as cool and interesting, the reality is far from this. 

Psychology is a difficult field unless you are genuinely interested in it and are certain about pursuing a career in it. A career is a long-term shot and you should be determined to go for a PhD from a top institute. Many times people are attracted to a certain field only to find later that they just wanted a way out of engineering. It's very necessary to do a self-analysis.

Also, I would like to clear the misconception that you don't have to get your bachelors in the same field as your master's. Unless you are planning to get a master's or doctorate, a bachelor's in psychology is not an easy degree to find a comfortable living after graduating. You can just take a minor in psychology in order to meet the eligibility criteria to enter many graduate school programs. But, if you want to pursue a research-based Ph.D. program you will likely need to get actual research experience, which may be harder if you only did a minor.

Additionally, you can read up on the latest research and articles in psychology, and explore different subfields of psychology, such as clinical, developmental, social, and cognitive psychology. It's important to remember that changing majors can be a big decision, and it may take some time to determine if psychology is right for you.