Oops, made a typo on the measurements.
The voltage at the front of vanagon
at both batteries is 14.02 volts, not 14.2
 Here are the corrected voltage measurements I get on
 my '90 westy with the 90 amp alternator.
 Engine compartment:
 voltage at alternator:             14.84
 voltage at battery 1 terminal: 14.14
 voltage at battery 2 terminal: 14.14
 on the isolator in engine compartment

 Front of the vanagon:
 voltage at aux. battery:          14.02
 voltage at main battery:         14.02
 voltage at outlet in dash:       13.95

Harald
'90 westy