" and now my batteries drain down in a couple weeks time."

Dave,
this may or may not be germain to your situation. I added gauges to my dash
top and used a + spade on the back of the main fuse panel. Little did I know
that these gauges constantly draw on an open electrical circuit and my
battery would run down in about 7 days. I fixed this by taking the steering
column shroud off and literally poking around near the ignition switch until
I found one that came on when the key is not, off when the key is off and my
problem disappeared.

your mention of "a good quality digital voltmeter" makes me wonder if this
is a hand-held instrument you use to check elec. circuits on your van, or if
it's a gauge you've wired into the "new" system and sits on your dash? If
so, this just might be your culprit .... I don't know?
Makes me wonder also what "accessories" you've wired into this battery. If
one of them has the tendency to draw current if it's available, like my dash
gauges, and may need to be "switched"?

Bob Stevens
'87 Westy Syncro
"Passion Fruit"