You could go to the connector at the ECU, pull the cover off and test the
middle green wire and the outter ground wire for continuity to each other
(this would show if the wires are touching somehow).  You could also test the
ground shield to ground to see if it is properly grounded.  You can get a new
one of these wires from a '87 Volvo wire harness if you have a local
U-pull-it wrecking yard this should only be a couple of dollars.  It even has
the same end in the ECU connector so you just pop it out of the Volvo ECU
plug and push it into the Vanagon one (sounds easy, get a couple of ice picks
to get that beast out).  See all the fun stuff you learn doing Tii
conversions :)

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242