I have a Necchi supernova Julia 534

http://www.necchimanuals.com/Necchi_Instruction_Manuals.htm

There is a button with two "prongs" or wings. Rotate the prongs clockwise about a quarter turn, to face the square mark (Q in the diagram) then press it down. It will stay down. To raise the feed dogs, turn the prongs anticlockwise (to S in eh diagram) and it will pop up
https://www.manualslib.com/manual/1205574/Necchi-Automatic-Supernova-Ultra-Mark-2.html?page=7#manual

Check here. Results are usually good.
Sewing Parts Online

There is a lever for positioning the needle bar. When you move the lever to the left middle or right , the needle bar too should follow the same. Try to do that. If it doesn't follow the lever and stays at one end, that means the machine needs to be oiled. Not like most sewing machines Supernova swings the bottom rod too to left and right when Zig Zag is engaged. I recommend to spray some WD 40 first, to inside of top and bottom side of the machine , and later to apply machine oil to every moving joints.

sounds like a sew-tric plug an motor if so under the motor's electrical connection cover there is a wiring diagram moulded onto it

call or email these sites and ask them
sewvacdoctor.com
a1sewingmachines.com

Try the Necchi Yahoo Group. There are members who often sell parts and they also are very knowledgeable and helpful.. You should also try eBay. They have parts for lots of vintage machines. You may not find what you are looking for right away but look often as things show up everyday.
https://groups.yahoo.com/neo/groups/Necchi_Pfaff_Sewing_Machine_Collectors/conversations/messages?messageStartId=9&archiveSearch=true

Contact Necchi directly (800-525-9987) and speak with the Service manager who may be able to get the part for you if they are available anywhere.
sewman7

Try ebay for a parted out machine.

All I did was google Necchi Supernova and the second link that came up was a threading diagram...