We sell a simple relay kit designed for this purpose, made by Hella.  It's tried-and-true (we've sold thousands of them over 15 years) and one of our most popular items.  It includes a fused relay, wiring, and instructions, and works in any Vanagon (Westy or not).  

http://busdepot.com/details.jsp?partnumber=1738

- Ron Salmon
  The Bus Depot, Inc.
  www.busdepot.com
  (215)  234-VWVW

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Toll-Free for Orders by PART # :  1-866-BUS-DEPOT