< snip> Could it have been that simple? A loose or poor contact or
corroded contacts on the Temp II switch? <snip>

Sure could.  In fact, the electrical connector at the temp II sensor
once provided me with an early warning that my water pump had just
failed.  It got doused with coolant and the engine started running
rough.  I pulled over to check it out (no overheating nor loss of
coolant light) and the water pump was leaking at a pretty good rate.  I
was able to top off the expansion tank and drive off the freeway (after
drying the temp II connector) to a parts place and effect the repair.

Mike
'84 GL 7 pass
'85 GL Westy