For the archives;

Synopsis;
86 Westy has intermittent oil pressure alarms (buzzer and flashing light) at LOW rpms, (clue; tach doesn't work)

Testing Performed;
Using Bentley's as a guide I do the out of van instrument cluster testing after I confirm light comes on with key, based
on my results I assume either board or circuit foil is bad.  I obtain new-to-cluster from Ebay, harass seller to ship 3-day 
(All Good Festival is Friday), and connect it up.  The tach doesn't work in new cluster, hmm....  Test tach with long test 
lead from coil and it works.  Run new tach signal wire to front, re-read Bentley's and determine I f-ed up testing of dynamic
oil pressure warning system.  Realized LED just flashed once with key on and went out, so bought new generic .3 bar sender from 
chain store (not in stock at dealer, but he could get me one for $25, I say no thanks and he counters with $20).  Install sender, 
cluster and fire van up.  LED blinks with key on, tach works, light and buzzer comes on with high pressure switch disconnected
and RPMs up.  All is Good.

Next week I plan to find out where the problem is with the original tach signal wire.  Now I have working warning lights, LCD clock, tach,
and all the tabs are intact in the new cluster.  I put the old speedo in with its lower mileage 80k vs 220k.

Moral;
Read that Bentley's carefully and do your steps in order, you'll save yourself some work in the long run.