Just to add a bit to the mass of information herein.  Didn't read the
entire thread but realize that there have been negative comments on
use of a-pillar for gauge installation.  Can't dispute the fact that
some folks wouldn't like gauges there but i've done several installs
on my own vans and for friends and the outcome has been very good.
And i really like the fact that i don't have to divert my eyes down to
view the oil pressure and temp gauges when installed in the pillar.
One other trick that i didn't see mentioned herein is using an outdoor
extension cord (typically has 3 shielded wires inside an external
rubber sheath) to carry your sensor signals up to the cabin of the
vanagon.  Works great and is much cheaper than purchasing separate
wire runs - plus you're double sheathed.

Here's some pics and info on installing gauges in the fashion i
mention.  All is related to having a suby engine in the back of your
van but the basics of mounting the gauges, running the wire, powering
the backlight on the gauges, and providing them with a ground is the
same with any engine.

go to http://www.weidefamily.net/vanagon/
then browse to Electrical > Gauges
or...hit this....http://www.weidefamily.net/vanagon/HTML/04/02/slideshow.html

and here's a bit more accumulated info on the subject....
http://www.weidefamily.net/vanagon/Pending_Content/Engine_Conversion/06RunWiresToDashAftermarketGauges/

all the best and good luck,
brent
--
Brent Weide
Portland, Oregon
www.weidefamily.net/vanagon/