I went through exactly the same drill you did.  My coil did not test
positive either.  After some time I found that the connections on the
back of the fuse/relay panel were corroded.  I would suggest that you
move the mass of wires around under the panel while you are cranking
the engine.   If the engine catches a few times then you have located
the problem.   I finally had to take the front seat out, get on my
back and work the connections around.  Also recomment ACF 50 to remove
and improve the metal to metal contacts.  The panel is a VW product
and is prone to connections corroding from heat, moisture and time.
After 25 years what would you expect?

Thanks for the info.

I got it figured out thanks to help from Noble.  I know it
didn't make much sense to me either so I took the battery and coil into a
dark room and sure enough it's working fine.  Must have been to much light
in the garage to see the spark.  So next I checked all the connection and
wires going to the coil and all checked out.  I then tried the light bulb
trick and I found that the neg wire to the coil wasn't getting switched.  I
took my scope into the garage again and hooked it up to the coil, nothing.
I did notice that it once spiked so I tried it again and this time I wiggled
the key as I was cranking and sure enough I got the signal that I was
looking for.  I next installed the plugs and sure enough as soon as I
wiggled the switch during cranking it started up.

Not sure if I'm happy to find the problem because of the work I now face in
replacing the switch.

I did notice that the tech isn't working now.  Any relation to the bad
switch?