However, when I apply for external jobs, they tell the prospective employer that I already have development work with them…and put into question my ‘sanity’ for seeking it elsewhere.
They have also falsely claimed that I regularly turn up late, and have health problems that I don’t have.
I take it you gave your current company as a reference? And I also take it they then try to abuse their position by giving false information?
Personally I would take matters into my own hands. Take it as a loss you cannot use them as a reference as they are trying to corrupt the proces, which is at the same time extra motivation to get out of the company.
In terms of recruiters or jobs looking for "simple" engineering practices, I'm not so sure. I think vocational school can teach these things (atleast in Netherlands on "MBO"), but a lot of people with this level of education do not end up as engineer but (field) technicians or in manufacturing or assembly. That is because a lot of companies like to get Bachelor+ people for anything that requires design or engineering, probably because EMC requirements or costly screwups in the case of an oversight.
At the company I used to work at, we also had these level of "one-off" jobs laying around, and most often we would get (MBO/Bachelor) students or internships to fix them up.
Nevertheless, not all companies are the same. Maybe there are companies around that have to fill these positions, but I'm unsure of any recruitment companies specializing in them.
My first bet actually would be to call up a few recruiters that specialize in electrical engineering jobs, and ask if they got contacts that may be interested.