There are numerous signals you could disable, power to the ECU, ignition
voltage, 
Wire between the ignition and the ECU, and so forth.
There are 'electronic keys' ....a simple device, that can disable up to 4 or
5 circuits.....
The 'port' for the key goes under the dash, you plug in the 'key' to enable
the circuits, and away she goes. 
Scott

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Richard A Jones
Sent: Thursday, November 15, 2007 11:31 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Fuel pump relay cutout switch

> Has anyone used another method of disabling the engine other than that one
> wire?

I have a fuel pump switch in my '81--installed for a
reason other than theft.  I got into the FP wire
at the FP relay, front, left of the engine
compartment and ran wires to a switch mounted under
the driver's seat:
http://jones.colorado.edu/jones/VW/VWfuelpumpswitch.jpg
(The other two switches control the cold start valve....)

Richard