We know it isn't easy to make a career shift like this when you don't have any real experience in the area in which you want to work, even though your associate's degree in electronics technology is related. You mentioned that you have been told your skills are weak when you have interviewed for positions that interest you in this area, which shows that you have an uphill climb in front of you.
It seems to us that you are really facing two major roadblocks: the lack of related experience and your part-time seasonal work for 15 years (perhaps left unspoken but certainty not forgotten by employers). We think this factor is actually the bigger roadblock of the two you face, as most employers are suspect of someone who was content to work for 15 years on this basis. Even though you mentioned that you tried to get on as a permanent year-round employee with the Internal Revenue Service, the fact that you didn't for all this time doesn't help your case, no matter what the reason for your not being hired as other than a seasonal worker. Employers will want to know why you didn't seek another full-time job when, year after year, nothing changed in your status at the IRS. They will also want some guarantee that you can be counted on to work full time, year-round for them if they take the risk to hire you with little or no experience — something that will be hard for you to demonstrate by your employment past.
So, the first thing you need to consider is how you will handle this issue and what you can say to help a prospective employer see there is reason to trust that you really want to work full time and year round. You will have to come up with some demonstrable proof that you can go the distance by referencing some other aspect of your life where you stayed the course over a period of time.
When you can overcome that hurdle, you can move on to deal with your lack of real-world experience. You will also need to be sure that the area you are choosing to focus on is a viable one. We checked with someone we know who has worked in this field for more than 20 years (with only a two-year degree and now earning well over $90,000 per year), and his comments had to do with the availability (or more precisely the lack) of jobs in assembly. Many of these kinds of jobs are being done offshore now as a cost-saving measure. When jobs are shipped overseas, it is nearly impossible for those without experience to land the few jobs that remain.
We think you will be better off focusing on one area that is in demand (perhaps CNC, calibration or inspection) than to have a myriad of interests/possibilities of what you could try. It's actually harder to find a job when you have too many possibilities than if you narrow down and chose one track (or two at most). You will be able to spend your time more productively when you aren't all over the map. Pick your area and pursue it with real determination and clarity. You will have a better chance to convince someone to hire you if you can show them your passion and dedication. This may be able to shift the odds in your favor, as some employers may be more open to taking a chance on someone untested knowing that these qualities will offset the lack of experience.
Finally, we have to agree with Paul HH when he says to start slow with real expectations (you surely won't come out of the gate making the top of the salary range!), and be patient and flexible. If you find you just can't make any headway, consider settling for a part-time job at the beginning, even though you want to get away from that ultimately. Search the ads and when you see one that you like, rush to the job location (the day the ad appears — do NOT send a resume) and offer your services as a person who could help them out immediately (starting that day if they like) until they find the right candidate. If you can convince them to give you a chance (even if it's only for a week or two) you may be able to show them you are the right candidate by hard work and initiative (and sidestep the issue of your 15 years seasonal employment). Even if they select another, you will have learned something and every bit of knowledge you acquire will help you to achieve your goals. You have nothing to lose by trying this approach.
Overcoming roadblocks is never easy; you will have to work doubly hard to do it. It can be done, but know that it will take time, commitment and persistence on your part.