I have had a 1940 Singer 201-2 on the bench for a couple of weeks. It was a mess and slowly it is being transformed.
The rubber insulation on the old wires had melted and run all over everywhere, including into the switch. The clear coat was flaking and the thing was filthy. The hook and bobbin case, however, were in great shape. They were donated to another 201. A beauty.
I took the switch out and started cleaning it today. I used some denatured alcohol on a q tip to wipe away as much of the black gunk as I could. I could tell that it was actually inside the switch mechanism because it had run out onto the darling little white toggle. I cannot believe that I did not take a picture of it.
It really isn't so hard to get the switch out of the terminal block
The first thing you do is remove the collar. Then you remove the nut. Then the switch pulls into the terminal block and you can remove it. I forgot, remove the wire connections from the pins first.
Once the switch is out, you can re-wire it.
First de solder the connection. I futzed around with a piece of wire braid on top of the old solder joint as I heated the connection with my soldering iron. I just could not get it cleaned up. Then I remembered that I had bought a desoldering bulb. Oh did it work WELL. (Max is sitting next to me and I must not use improper grammar but I so wanted to say GOOD.)
Next I prepared my new wire. I do like to make home made wire ring connectors vs crimping on the commercial connectors. Personal preference. I solder the ring just because it is so much fun. You don't really need to.
I put some red heat shrink on the end to identify this as the red lead.