These are tutorials on specific aspects of sewing machine repair that I’ve found helpful in my work on old machines. More to come soon!
Electric, Wiring, Motors.
Electrical systems and safety from The Archaic and the Arcane: http://www.archaicarcane.com/love-becomes-electric-electrical-safety-and-your-sewing-machine/
The Vintage Singer Sewing Machine Blog on how to rewire a potted motor (info very applicable to other types as well): http://vssmb.blogspot.com/2012/01/complete-how-to-re-wire-potted-motor.html
Wiring diagram for vintage Featherweight style Singer plugs: http://oldsingersewingmachineblog.com/2012/03/28/wiring-diagram-for-vintage-singers/
ISMACS Singer wiring diagram: http://ismacs.net/singer_sewing_machine_company/manuals/sewing-machine-wiring-diagrams.pdf
a word is elegy to what it signifies 
i need Model 740,BERNINA-Favorite part list Needle displacement lever.
hard to move on left.
I don’t know of anywhere to find that particular part, but I’ve had some luck oiling stuck parts, then using a hair dryer to heat up the area, then let it cool again, oiling and repeating the process a few times. It makes the metal expand and shrink back just a little bit, which can help oil get between stuck parts. If not, ebay or etsy might have the part you need.