Matt,
  I had this problem a couple of years ago with my '91.  That cable is
made of such fine strands of wire that it corrodes very easily and turns
to powder.  The original ground strap on the left side of the engine has
the same problem.
  When I took mine to a rebuilder, they said they had to replace the
field coils so it cost me a little more than the usual rebuild.
Everyone should be sure to apply grease or something to protect that
short little cable between the solenoid and the starter body; it has to
handle a lot of current.
Good luck,
Larry A.

Matt Sutton wrote:

>Hi Folks,
>
>    On a trip to Philadelphia the other day, the van refused to start or
>even turn over after a rest area stop. Tried jumping it, even though there
>were 12.5 volts at the battery, and got nothing. Eventually we got it
>running with a push start, with help from some repo guys who were towing the
>truck next to us.  The next day I found the short wire from the lower
>solenoid terminal to the starter to be corroded beyond repair; it just
>crumbled as I tried to clean it.
>    It seems like the solenoid is still functional (it clicks when I try to
>start), so maybe I really just need to replace that wire that terminates
>inside the starter motor. Looking at the Bentley, it seems like the wire
>feeds the field coils of the motor. Can this repair be done? Has anyone done
>it? Any educated guesses about what gauge wire to use, things to check/worry
>about while the starter's apart, etc. would be much welcomed.
>
>Van info: 88 Gl, manual trans, approximately 220k on the original engine,
>though by the look of it the starter may be a rebuild.
>
>Thanks,
>
>Matt Sutton
>Brooklyn NY
>
>
>