You could wire the relay to the "x" circuit if you want the second batt to 
not connect when cranking. (same as the headlamps do)

This way it would not draw on the main during start, still auto charges,
and not be linked when parked. 

A 3 pos switch gives you the best option however, as you can boost from 2nd batt if needed. 

Pos 1 linked together
Pos 2 never linked
Pos 3 only linked when key is on. 

If you have volt readings on both you can tell if 
the 2nd batt can assist in a start or not. 

  ----- Original Message ----- 
  From: Dave Vickery 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Thursday, January 12, 2006 7:09 PM
  Subject: Re: 2nd Battery setup questions

  I think the idea is that the relay is activated by the alternator charging,
  not just the ignition key being turned.  That prevents the run-down battery
  from robbing power from the charged battery when you first turn the key but
  aren't charging yet.

  But I am not 100% sure this is how it was designed but I think so.  I just
  put a second battery in and am puzzling over the same thing.  I may just put
  in a manual switch.  When you run wires, you would run them under the van
  which is no big deal.

  Anyone else?

  Dave in Denver

  >From: RoadwarriorSF <sfwesty@GMAIL.COM>
  >Reply-To: RoadwarriorSF <sfwesty@GMAIL.COM>
  >To: vanagon@GERRY.VANAGON.COM
  >Subject: 2nd Battery setup questions
  >Date: Mon, 9 Jan 2006 17:51:22 -0800
  >
  >This is for a 91' Multivan
  >
  >Has anyone setup their 2nd battery using  a wirewerks kit? (this one)
  >http://wirewerksperformance.com/index.php?main_page=product_info&cPath=31&products_id=10&sessid=a9494efc0ab583f5e3d8f390e3edff8c
  >
  >Maybe this is something the list can help with. This kit's relay requires a
  >connection to the "no charge light" wire coming off of the alertnator. It's
  >used to "power" the kit according the wirewerks folks. I wondering if I
  >really have to run the wire back to the alertnator? If so, is there an easy
  >way to get around the bench and through the engine cover? Shouldn't the
  >wire
  >terminate at the front of the vehicle? Wouldn't that be easier?
  >
  >Here's the schematic
  >http://wirewerksperformance.com/images/Schematics/aux%20battery%20charge%20kit.doc
  >
  >Thanks,
  >Yoel and Tina