Hi Ian.  As Jim, states,   there is a box in  the westy linen closet 
that has to come out to gain access to the 2nd valve.  

Hope this helps,
Harry

> I think this may be where your problem starts.  My 87 & 88 Vanagons have the
> second port inside the plactic cover that runs from the floor to the ceiling
> at the left/rear corner of the van.  You can remove the cover easily with
> about 6 phillips-head screws.  I would bet that your 1990 model DOES have two
> ports and that you need to uncover the second one.
> 
> Good Luck,
> Jim Davis
> 87 GL Syncro
> 88 GL Wolfsburg
> 
> 
---------------------------------------------------------
Harry Yates, Langley, BC, Canada
'90 Syncro Westfalia www:   http://www.bcit.bc.ca/~hyates
'87 Golf Diesel      email: hyates@bcit.bc.ca