Success :)   for the archives -- the problem was the T14/3 connector
was dirty/oxidized.  I discovered this after bench testing the
instrument cluster and finding it worked properly after making good
connections to 12V and ground.    Some rubbing with a pencil eraser
and gentle scraping with a screwdriver on the connector cleaned it up
enough to work.  I'm still not understanding why a bad ground would
cause the high beam LED to light, but I guess that's just one of
life's mysteries.

Thanks again to all who offered suggestion and advice, it helped keep
my motivation up for solving this gremlin.

On Dec 22, 2008, at 10:20 AM, Michael Diehr wrote:

> 1985 Westy -- just last night started misbehaving.   Symptoms:  with
> ignition off + headlight switch on, three LEDs in the dashboard glow.
> With engine running + headlight switch off - normal.   Engine running
> + headlight switch on, all dash instruments (including lighting) go
> dead.   The load reduction relay seems to work fine (e.g. headlights
> on + ignition on = headlights work, and when you crank the starter the
> headlights go out).  Toggling high beams doesn't do anything weird.
> This sounds like a ground issue from a failing headlight switch?
> Wiggling the ignition key doesn't seem to change anything in any
> state.
>
> Unfortunately the van is about to go on a long trip, so need the part
> asap etc.  Are there any surefire diagnostics I can do?  I have
> voltmeter & bentley.  Thanks!