My 81 aircooled California van certainly does have the shielded cable.
In fact, someone had replaced the connector and joined the shield and sgnal
wire together.
This had the effect of grounding the signal voltage input to the ECU. Made it
hard to smog and brought the price down.
    Peel the connector cover back on the green wire and you should see the
shield itself or a bump under the insulation about an inch back from the
connector.
    If you put a voltmeter on the connector and measure to ground while the
engine is running you should see a variation of several tenths of a volt
around 0.5

Steve
Mytle the Turtle '81 Vanagon