You should NEVER swap up to the next size fuse, when any type of circuit fault causes the correct size fuse to keep blowing.  
  The fuse rating is engineered to blow at nearly the maximum current-carrying capacity of the wire.  If you add a greater load to an existing circuit, and that causes the original size fuse to blow, that means that the wiring is pulling more amps than the wire size is able to safely handle.  If you proceed to install the next-size-larger fuse, you now have created a fire hazard that could cause a total loss of your treasured vehicle.  When a wire draws too much current, it gets hot, melts insulation, the copper can even glow like lightbulb filament along its entire length!  Not good!  At this point the wire becomes the weakest link and 'blows' instead of the fuse!  Ii's also capable of filling the vehicle with noxious smoke and fumes.  Do you want to keep your family in this vehicle?  I can't recommend it.

Mike B. (licensed FAA aircraft mechanic, and licensed electrician in 2 states)
  ----- Original Message ----- 
  From: Al Knoll 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Tuesday, September 29, 2009 7:09 PM
  Subject: Re: No High Beams

  Actually, Rocket J. you can discern the wire size to the brake lights by
  gazing at the current track in the bently. With that in mind you can
  estimate the current carrying capacity, then see if the total draw exceeds
  the reasonable capacity of the wire.  If it does't then just fuse to the
  next higher value.  If it does exceed the RCOFTW by some you might have to
  run a second circuit.   Works for all accessories of course.

  Pensionerd.

  On Tue, Sep 29, 2009 at 7:20 AM, Rocket J Squirrel <
  camping.elliott@gmail.com> wrote:

  > Along those lines, I instantly blew the fuse for the brake light circuit
  > when I connected up my little trailer and tested the lighting. Not a
  > miswiring, just the additional load of the trailer's two little brake
  > lamps was sufficient to pop the fuse. VW must rate the fuses pretty close
  > to the expected load current so even a non-shorting fault is sufficient to
  > open the fuse. Had to swap up to the next-sized fuse there.
  >
  > --
  > Mike "Rocket J Squirrel" Elliott
  > 84 Westfalia: Mellow Yellow ("The Electrical Banana")
  > 74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
  > Bend, OR
  > KG6RCR
  >
  >
  >
  >  On 9/29/2009 4:15 AM Frank Condelli wrote:
  >
  > In a message dated 28/09/2009 3:14:30 P.M. Eastern Daylight Time,
  >> LISTSERV@GERRY.VANAGON.COM writes:
  >>
  >>        If you were to read my _Headlamp Relay Upgrade_
  >> (http://frankcondelli.com/hdltrela.htm)   webpage.  It specifically says
  >> that it is necessary
  >> to change the 10 amp  fuses to 15 amp when installing the higher wattage
  >> bulbs.
  >>
  >>
  >>
  >>   Mark Drillock got it, right on the  button.  Both fuses 9 and 10 were
  >>>>>>>
  >>>>>> blown.
  >> I guess those little 10 amp  fuses don't like the bigger lamps I have in
  >> both
  >> units.  And since I  drive at night very seldom they could have been out
  >> for
  >> some  time.<<<<<<<<
  >>
  >>
  >>
  >>
  >>
  >> Cheers,
  >>
  >> Frank  Condelli
  >> Almonte, Ontario, Canada
  >> '87 Westy & Lionel Trains (_Collection for sale_
  >> (http://frankcondelli.com/trainsal.htm) )
  >> _Frank Condelli &  Associates_ (http://frankcondelli.com/busindex.html)
  >>  -
  >> Vanagon/Vanagon Westfalia Service in the Ottawa Valley
  >> _Vanagon Stainless Steel Exhaust  Systems_
  >> (http://frankcondelli.com/exhaust.htm)
  >> _BusFusion_ (http://www.busfusion.com/)  a VW Camper  camping event,
  >> Almonte, ON, June 11 ~ 14,  2009
  >>
  >>