Thanks Alistair for posting revealing pics on the interior of that Rear Window Defogger switch.  It may be "possible" to install a modern tiny LED to replace the incandescent bulb and light pipe combo, but I've kind of decided against it (for present project purposes, I can always add later).  I just don't want to add another failure point mostly.  For my project, the switch will mostly be actuated in daylight hours making it a little hard to see anyway.

Oh...what is the "project"?  I have this hot shower rig in my Vanagon; I utilize the rear heater hoses lines (heater long gone) to feed a 1/4" x 20 Feet Copper Coil.  This coil sits inside of a 5 gallon (20 quart) thick-walled aluminum stockpot from Costco.  Previously, I would run back to rear of Van and open ball valve; hot coolant goes inside copper tubing heating up water; BBQ thermometer with wires up to cockpit monitors water temperature.  Alarm signals at 122 °F.  I then pull off highway, run to back of Van again, and close ball valve.  Super simple.  But sometimes, enough times over the years that this running back and forth to open and close the ball valve got to be a pain.  Solution?  Motorized ball-valve, with auto-close when power shuts off.  And so the whole purpose of utilizing the spare rear defogger switch is to open and close the ball-valve.  I'm almost done with the project; last step is to install switch in instrument cluster, add an-inline fuse, and wire it up.  Should be cool.  I mean....hot!
Rich
San Diego

    On Saturday, April 4, 2020, 10:57:34 AM PDT, Alistair Bell <albell@shaw.ca> wrote:  
 
 Took apart a spare switch I had. Posted pics 
https://shufti.blog/2020/04/04/vanagon-inside-the-rear-window-defogger-switch/

Just to further the discussion :-)

Alistair