This is a good question, and it is really quite simple. If I were you, I would do what I did and find an entry level position at a shop. It may be a bit difficult at first and you may have to stray away from your traditional "diesel" shop and look for an automotive dealership (one that offer a diesel line, of coarse). The airport is also a good place to look into, I worked on the big equipment there and they had entry jobs with the smaller equipment for the younger techs just coming into the field. Once you find your position and gain some experience, that may help you determine a path you may want to follow. Like one of the previous comments suggested, "Electrical" 100% true, but that is also learned with time and experience and if you want to make money, there are many other aspects of the job you need to know as well.
Now start looking for education, a good school will teach you the basics, like the electrical and mechanical components. I worked at a dealership for about 1 year while I looked for a school, trust me, this will help teach you more and once you get the education it will help get you better jobs and more money quicker. I decided to go to one of the large colleges (UTI), but I believe the right community college with a basic automotive/diesel course would be just as good.
Once you are in the field, be aware of yourself. In my 15 years in the industry have taught me, stay humble, because you will never know it all and the guys who think or tell you they do, take their advice with caution. Never be afraid to ask questions or take advice, even if you believe the way you do things is better, try a different way, you may find you like the new way and believe me you will never stop asking questions. Take your time with your work and never rush, the major draw back in this industry is the expectation to finish as fast as possible or "flat rate" the job, this is how major mistakes are made, especially early in your career, trust me, you do not want to become a "hack" technician, they are the guys who still give us good techs a bad name, you will get faster with time, do what I still do and work at your own pace.
Remember, if you really want something, make goals, work hard and you will get it. I met my original goal to work on Exotic, high-end and classic special interest vehicles, If I can meet my goals, anyone can!