How should I make a secure joint between this switch and the ground wire behind the doorjamb? (I tried solder and melted the plastic part of the last switch.)

 

Clamp the end part around the wire and add a little solder. If you solder the wire end first and make sure that the switch end is clean, it should take a few seconds to solder it together.

 

The edges of the hole in the jamb need to be clean to make the switch body earth properly - the lead is always hot, and its the earthing that brings the light on.
jp 83 Euro S AT 51k

 

Take it apart before soldering. I took fine needlenose pliers and a mechanic's pick and uncrimped the connector to remove it from the plastic piece.

Then, made the solder connection to the connector.

Then, re-installed the connector to the plastic piece.

I did three of these on the 84. Looks like the piece you photographed is the same.

The door threads were not an issue for me, when cleaning-up an old switch. What was an issue was corrosion on the edge of the crimped connector that must contact the threaded metal part of the switch.

 

Aryan, that sounds like what I did that melted the last switch.

jp, I will doublecheck.

Chris, that sounds like a better idea than what I tried last time, but I was hoping there was some magical connector that goes on the wire and plugs into the switch.

 

Maybe something exists, not sure.

I've taken to soldering all connections that I can get at. Am using a straight propane torch because I can't seem to properly use a solder gun.