Many Westfalia, weekender, and multivan vanagons have problems with their alternator charge light staying on or at least partially lit after the subaru engine is in place.  The cause of this issue is that the circuit which feeds the idiot light also feeds other loads.  The fluctuating load on the circuit causes the light to come on partially or fully.  If the circuit is dedicated to the idiot light, the issue goes away.
The method of dedicating the circuit originally came from KEP and they should be given full credit for the idea.
Here's how it's done:

Begin by removing the fuse block facia.  It's a piece of rounded plastic held in at each side.  Push it in and up to remove. 
Now, remove the two screws that hold the entire fuse panel bracket in place, plus the screw that fixes the panel to the bracket.  The entire fuse panel assembly can be dropped down and made fairly accessible.
Carefully twist the panel around so that you can view the back of the panel.  Note that there are several groupings of wires across the back of the panel.  You'll see that each of the groupings are lettered if you look closely enough.  This is also a great time to break out the vanagon manual as they may have pictures with labels on them.  You are looking for terminal block A, terminal block E, and terminal block B.  There's a couple of blue or green wires that run to terminal B1.  One of the wires runs out to A16, the other to E13.  Cut the one that runs to A16.  Cut it at a point about 1" from where it exits terminal B1.  Take the remnant of the wire which is now only anchored to A16 and run it to one of the ignition on power source spades at the left side of the back of the fuse panel.  Crimp or solder a female spade connector onto the end of the wire and tie it into one of the spades.  Now you should be able to remove the blue wire from the refrigerator power relay under the driver seat and your alternator, although still functional (test by turning the ignition key on, but not starting) will not remain lit after the engine is started.

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