I'm offering this solution for archive purposes and as info for list
readers. Thanks to all on the list who helped me track down the problem!

I fixed the radiator fan problem in my 87 Westy Syncro (after replacing a
bunch of parts I probably didn't need). Here's what I found:

First, Ken's trick of jumpering finally worked. The fan came to life,
indicating first that it wasn't the fan motor. But strangely, the jumper
would only work kind of hit or miss.. once it would work, then it wouldn't.
Hmm.. sure seemed to indicate that a short was happening somewhere.

I broke out the Bentley's and figured I'd check all the relays and fuses one
more time. In looking at the Bentley's I noticed the diagram for the back
connectors to the fuse & relay panel. I figured this might be worth checking
to make sure everything was in fact plugged in right (especially since all
the fuses did in fact check out).

I unscrewed the fuse panel, and found the T type plug which connects the
panel to the wires going to the radiator switch. Everything looked OK. Then,
I happened to see two star shaped brass units which served as a hub for all
the grounds, behind the fuse panel. Hmm... if its a ground problem, maybe
this is worth some inspection...

Each star unit had male plugs for approx ten female ground connectors, and
was then screwed to the firewall. Of the two, the first one closest the fuse
box looked just like brand new. The second, however, had significant
corrosion on the rear posts.

I took all the connectors off and then using a wire brush mounted to a
dremel moto tool, I cleaned each post and each connector. Put everything
back on, cruised around to get the engine hot, then let her heat up at
standstill. Just as things started to get hot I heard the sound I was
looking for.. the radiator fan coming to life! Cooled everything down just
fine. Tried it again for good measure, and the thing even worked after the
engine was shut down.

Crisis of the moment solved!

Bill