Volks,
 
I've got an instrument cluster swapping problem that differs from the norm.  I'm hoping it can be resolved simply but I've got my doubts.  Hopefully somebody has dealt with this before.  He we go...
 
My sons '87 GL came with a tach.  About a year ago I swapped that cluster for the clock cluster in my '86 Westy.  So far so good.  Swapped the speedos and everything worked as expected.  
 
Now I've picked up another cluster supposedly from an '85.  The date stamp says 11/84.  I swapped it into his van and I get a blinking water temp light.  Everything else appears to work.  It's apparent these clusters are not the same in construction besides the obvious tach vs. clock difference.  The '86 cluster (date stamped 2/86) has a circuit board inside the speedometer whereas the '85 does not.  The '85 has circuitry for the digital clock and of course the '86 doesn't.  The van has a yellow wire at position 12 on the wire harness.  The piece of harness still attached to the '85 cluster had no wire in that position.  I did not have a chance last night to try and identify the yellow wire in the Bentley.
 
If you're still following this, I'm guessing that the circuit board in the speedo is related to the later oil presure system.  For that reason alone I'm guessing this cluster can't be made compatible.  I'm also guessing that the yellow wire is coming from the coolant tank sensor and that this might have been new in the later models.  Just guessing.  Any way, is there anyone out there that has a solution to this problem that doesn't require major surgery?  If not, I guess I'll be selling or trading an early model tach cluster for a late model unit.
 
Thanks.
 
Jeff Warner
Galloway, OH
'86 Wolfy Westy "Barry"