My only concerns is that, the hiring manager may not like it, if he/she founds out that I conduct freelance activities while working as a full time engineer for another organisation.
Do not include the freelance work in your chronological employment history. Instead, append another section and title it "Personal Projects". Detail each project separately, but do not include any dates or indication of freelance payments or conditions.
Focus on describing what you achieved doing that work. Avoid speaking in terms "for the client" and think in terms of benefits you yielded.
There is huge value in a technical person who can sit down with another human and communicate wants/needs for a project. Try to see how your freelance experience demonstrates you are a nice person and not just technically skilled.
the job that I am seeking are more related to my Full time job, but I wish to highlight my freelance job in my resume
Only include freelance projects that directly relate to the job you are applying for. Exclude others if you know they are not related.
If you are posting this resume on the Internet, and you do not know who will be reading it, then include all your projects, but when you are applying for a specific job filter the content.
Think in terms of risks
The employer is engaged in risk management when hiring a new employee. For them, there are many risks that the new hire will not work out. Try to keep this in mind, and work to actively reassure them there is no risk.
- You were not freelancing because you were underpaid. You would do the work for free.
- You did the work for the enjoyment of it, and not because you disliked a day job.
- If asked, you did freelance when employed and you learned many new things that directly related to your current job. Share an example of that fact.
- Reassure them that you've never been tired at work. Started each day on time and refreshed.
- If asked why you did the projects. Explain that you did it to help others and share examples of projects and how they helped change lives. (i.e. a client was struggling to grow his business online, and your work helped relieve that stress and worry).
They are simply afraid of making a hiring mistake and might not directly say it, but they are thinking it. Be proactive and help them see their fears are unfounded.
Ask a friend or coworker to review your resume. Be very specific. Do you see anything here that would be a red flag for a hiring manager?
Often we can't see the negative aspects of our resumes as we're too emotionally connected to it. Remember that it's perspectives and not facts that are important. If in doubt leave it out.
Keep in mind that the job of the resume is to get the interview. It's in the interview that you have a conversation. So no red flags in resumes. Just positive signs that you're a smart, skilled and friendly person.