RE: 12v Grounds for Accessories
Some are going to argue that I'm overdoing it and that using chassis ground
for accessories will work fine.  BUT, having had a really good education of
grounds and ground loops back in the '60's (analog computers) I have a
simple answer:  Run a separate ground for each circuit and ground everything
at the same point.  I don't tap into any existing circuit if there is any
way to avoid it, I run a double wire, hot and ground, to whatever I'm wiring
in. All accessories added come out of a fuse block on the cabinet wall
behind the drivers seat.  That is fed directly (through a 40 amp breaker)
from the aux battery.  Right now I have a ground buss set up and mounted
next to the fuse block, soom to be incorporated into a new, better fuse
block that will replace the current setup.  In a previous life ('85 Westy)
the PO had added two lights in the back, good halogen lights, plenty of
illumination.  But, they worked sporadically and never when you really
needed them.  When I got around to troubleshooting them the problem was
grounds.  The DPO had assumed that he would get a good ground through the
mounting screws that went into the body of the Vanagon.  Once those grounds
were fixed no more problems.