The switch has most likely passed on, I doubt it has anything to do with air in the system so only option is replacement. Have had this happen to me before. When you get it off you can poke a matchstick down the hole at the back to see if you can get it to activate.
Re. your soggy front brake lever, I can relate that recently I replaced the caliper on mine with a good used one from a member here. The brake bled right up and I've never had a firmer brake lever. Go figure, I did exactly what I've done half a dozen times before and the result is just better, I didn't touch anything but the caliper leading me to think there was something wrong with the old one.
P.S. Enjoying what you are doing down there, I'm from Cape Town myself, now resident in Denmark.
The switch, Henning, is a new one; I used it instead of the original during the rebuild. Maybe I'll try the old one, if I can find it. I was also thinking of trying a different capiler, but the old pad/cylinder is
stuck in there. The weather here is still better!

Did you do the whole "bike on sidestand bars locked left lever ziptied half-back over night" trick?
Give that switch a few taps with a rubber mallet or screwdriver handle and it should pop the air bubbles out with the bike in that position. It should no affect the switch's operation.
Have you checked the switch for continuity with a voltmeter when you squeeze the brake lever?
Haven't tried it with the bike on side stand, but I've done everything else. Will give it a go.
Lone Builder, I had a similar problem and it turned out to be broken wires in the harness. The copper strands were broken inside the plastic jacket: the wires looked ok, worked ok sometimes, but tested bad when flexing the brake light wires.
A couple butt splices and some super flex wire and it has been good for 15? years.
I have also had success with evanphi's tie the lever back method.
...and, nice photos at the lake. Extra quiet places are super.
The wiring is Ok, Kevin. Jumping the connections lights up the light. The harness has been "sorted" during the rebuild.
Seventeenth century French scientist Blaise Pascal is perhaps best remembered for his contributions to the field of pure geometry. In the 39 years that he lived, he found time to invent such modern day fundamentals as the syringe, the hydraulic press, and the first digital calculator. And, if that weren't enough, he was also a profound philosopher. He said,
"All man's miseries derive from not being able to sit quietly in a room alone."
Perhaps if he had a lake to sit beside ...
Sean