All dash lights have gone out. Rotary dimmer dial still dims
radio lights
        They are fused, to my knowledge, with back-up lights which work.
        Bulbs' filaments are intact. Anyone else had this occur?

Same thing happened to me. What I found was the connector between the
speedo/tach assembly and the ribbon cable had become corroded. What you
need to do is pop off the top of the instrument panel, unscrew the
cluster assembly ( you are going to have to pop out the hazard light
switch, light/dimmer switch, etc. to be able to fully remove the
instrument cluster). Now unplug the ribbon cable from the cluster. If
your connector is like mine (85 Westie) it will be black with corrosion.
I used Emory paper to sand it clean but you can also use some kind of
electrical contact cleaner. All clean now? Test it before you put it all
back together ;-)

Hope this helps.

Scott Semyan
'85 Westie
Seattle, WA