[W126 Coupe] tach not working

[IHouse]

Hi folks,  I let my battery run down and after putting a charger on it 
(foolishly I did not disconnect from the car), I find the tach no longer 
works.  I'm not sure about the fuel, oil and temp but I think they are 
not working either. (oil gauge is pegged, fuel slightly below half and 
temp at bottom of gauge)  I checked infamous fuse #6 and have 
continuity, the front overhead lights work also so I'm reasonably sure 
it's not that fuse at least. The dash lights and center control lights 
work so does that mean it likely isn't the fuse on the back of the 
instrument cluster?  I read in the archives it could be a ground problem 
to the cluster.  Any ideas what to check next?

Thanks,
Ike

87 560SEC