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!