Thanks for saying what you are trying to accomplish.
Your idea is sound, and you could interrupt any of 3 wires at  the fuel pump
relay,
 - the 'supplies ground' signal from the ECU.
 -the power supply wire to the relay,
 - or the 'hot signal coming out' wire that goes to the fuel pump. 
I'd access the fp relay in that black box above the coil, figure out which
is the main relay and which is the fuel pump relay and proceed carefully.

It really is clearly indicated in the Bentley current flow diagrams, tho
they are funny to read at first for sure, but if you find the current track
for 'fuel pump' .....you should be able to see the pump, and the relay, even
how it works internally, if you understand the basic principle of a relay
anyway. .  They don't always show things really well, but on these basic
circuits, they're ok. 
Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David O'Bryan
Sent: Wednesday, November 14, 2007 3:01 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Fuel pump relay cutout switch

Help.  I'm helpless when it comes to reading a current diagram (but I really
did try).  I want to install a cut out switch on the wiring to the fuel pump
relay and cannot figure out which wire from the ignition switch area will do
that.  I want to run the lower power wire that energizes the relay thru a
switch as an anti-theft device.

Any help is appreciated.  :-)

Regards,

Dave O
'87 Westy