I have a twin to yours. It's pre 1949-50. At that time the V was dropped in the logo, so any machine with the VN is older than that. There doesn't seem to be any exact dating technique because Necchi didn't keep the detailed records that Singer did. My Necchi sews perfectly. When my 301 was down, it was the only other machine in the house that would FMQ nicely. Miss Sophia is in a cabinet with a knee control.
It doesn't look like your plugs are original to the machine. I'd take them apart and make sure all the wires have good contact with the terminals. It sounds like you have a loose connection - no, not you, your machine. Whoops!