Here is a generic diagram of how the Singers should be wired. Even though they don't look exactly like this, this is the way to do it.
It might be the same as your electrical engineers drawing, but it don't look like it to me.
If your 66 is completely OEM, I have a factory wiring diagram for it. I can't post it here as it's an old copyrighted drawing and I've had the moderators delete my posts due to that. If you want that diagram PM me your email and I'll email it to you.
Joe