well.........
I have a trailer, it's brake lights don't pop fuses on the stock brake light
circuit,
( a volvo, not a vanagon, fwiw )
nor is that a common problem.

you don't have 6 volt bulbs in the trailer do you ?  ( I doubt it ! , just
checking )

well, some might scream, but I bet, IF THERE IS NOT SOMETHING WRONG or WEIRD
somewhere, you can run a 16 am fuse on that circuit.

Though I *waould be suspecious*  , because just hooking up trailer brake
lights to the stock circuit is usally not a problem, far as I know.
I'd check things carefully, all wriing carefully.
I run a dedicated ground wire for my trailer, even though it will usually
ground through the hitch.

do the lights flash extra brightly before the fuse pops ?

----- Original Message -----
From: "Rocket J Squirrel" <camping.elliott@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, September 29, 2009 10:43 PM
Subject: Re: No High Beams

> I'm not sure what "mismatched ground levels" means, but the trailer wiring
> and the connector wiring in the van are new and clean.
>
> The facts are these:
>
> 1. With the trailer connected, and a new stock 8A fuse, the brake lights
> flash only very briefly before the fuse pops -- I've done this a few
> times, it's what happens.
>
> 2. If the fuse-poppin' overcurrent were due to a short, the lamps would
> not flash at all.
>
> 3. Since they did light, the current was going through them.
>
> 4. Since the fuse popped moments afterward, the current was higher that
> the 8A rating of the fuse.
>
> 5. Calculations, courtesy of Hr. Dr. Ohm, give us 7A for four 21W lamps in
> parallel. Just short of the fusing current of the stock fuse, so if it was
> going to go it would have done so after at least several seconds, not a
> bare moment after power had been applied.
>
> What fits the facts is this: my Inrush Current Theory*: Yes my word you
> may well ask what it is, this theory of mine.  Well, this theory that I
> have -- that is to say, which is mine...is mine. And this theory of mine
> is this: four 21W bulbs in parallel will draw anywhere between 36A to 72A
> for anywhere between a few tens of milliseconds to a few hundreds of
> milliseconds, which is plenty strong enough to fuse a 8A link. But not,
> apparently, enough to fuse a 16A link.
>
> Vanagon content: this is part of a thread that is discussing the safety of
> putting on increased loads on the old wiring in our vans.
>
> ==========
> * Yes, the hypothesis, Dear Dr. Feynman.
>
> --
> 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 9:11 PM Al Knoll wrote:
>
>> Hey, you're right, could be an intermittant short.  Only happens when you
>> hook up the trailer.  Mismatched ground levels?  Hard to say without
>> data.
>>
>> One small matter that needs clarification.  The corrosion of which you
>> speak
>> in glowing terms actually increases the resistance of the circuit.  Since
>> it
>> is a simple single loop current path and the supply voltage is not
>> varying,
>> the added resistance actually lowers the loop current.  Not likely to
>> melt a
>> fuse specified for a lower resistance load.  The connector junctions will
>> heat up and melt but not because of additional current through the loop
>> unless of course there is some sort of short to ground making a two loop
>> circuit.
>>
>> However, like Dr. Feynman is noted to say "no matter how elegant the
>> hypothesis, or how eloquent it's presentation, if it doesn't agree with
>> the
>> data, it's wrong"
>>
>> I don't have the data on the electrical banana but I do have the
>> credentials.
>>
>> Takes a double 'ee' to make a dweeb.
>>
>> Pensionerd. Geeky Dweeb in thin disguise.
>>
>> On Tue, Sep 29, 2009 at 6:37 PM, Mike <mbucchino@charter.net> wrote:
>>
>>>  It's not as much about in-rush, start-up current or even continuous
>>> current draw in a normal circuit.  You could install a slow-blow fuse of
>>> the
>>> original rating to counter start-up in-rush currents.
>>>  But, now factor in corroded contacts in the bulb sockets, poor
>>> grounding
>>> (both common complaints on our older Vanagons), and corrosion that
>>> 'wicks'
>>> up into the wire strands on the ends (invisible under the insulation),
>>> and
>>> it all adds up to more total, continuous current draw.  This gets the
>>> entire
>>> circuit warm (even hot!) and will break down insulation and plastic
>>> parts
>>> over time (remember how our headlight switches melt down even with an
>>> all-stock circuit?).
>>>  You need to do an actual ammeter measurement on the van, not a
>>> theoretical
>>> mathematical calculation based on book and diagrams.  Your circuit is
>>> far
>>> from new and is now modified from stock.
>>>  When a conductor shorts to ground, accidentally, anywhere along it's
>>> entire length, you now have a wire that'll blow (and WILL glow!) before
>>> the
>>> higher-rated fuse will blow.  As I said, it's not a good scenario, no
>>> matter
>>> how you like to ratonalize it to yourself.  You MUST upgrade the
>>> conductor
>>> to a larger cross-section to prevent this possibility.  Alternatively,
>>> you
>>> could also add another conductor, in parallel, alongside the existing
>>> wire,
>>> but I don't like that idea much for a couple of reasons (what if it come
>>> apart somewhere?).
>>>  Also, your wires are not running in "free air", but are cabled in a
>>> harness alongside conductors, and thusly, the circuit needs to be
>>> 'de-rated'
>>> accordingly.  This means that your calculations are wrong, so, an
>>> engineer,
>>> you're not!  (neither am I, but I use my 'book-knowledge' and real-world
>>> experience to guide me in making decisions to 're-engineer' things
>>> sometimes....)  Hope I've explained it properly.
>>>
>>> Mike B.
>>>
>>>  ----- Original Message -----
>>>  From: Rocket J Squirrel
>>>  To: vanagon@GERRY.VANAGON.COM
>>>   Sent: Tuesday, September 29, 2009 8:58 PM
>>>  Subject: Re: No High Beams
>>>
>>>
>>>  I don't dispute your knowledge and experience.
>>>
>>>  Let's see how closely VW cut things.
>>>
>>>  97.58 (Bentleys) shows the brake light switches fed by a single 18
>>> gauge
>>>  wire through a 8A fuse (S8). 18 gauge wire is rated to carry 13 amps,
>>>  continuous, in free air, forever, if it has insulation rated for 60C.
>>>  There are insulations rated for higher-temperature operation, and the
>>> wire
>>>  can be run up to 18A or more with better insulation. But I don't know
>>> what
>>>  kind of insulation is used in the Vanagon, so I'll use this rating, the
>>>  most conservative I could find.
>>>
>>>  The two brake lights on the Vanagon are 21W, so they each draw 1.8A,
>>>  steady-state, although the turn-on surge of a tungsten filament can
>>> exceed
>>>  the steady-state value by 5 to 10 times because a cold filament has
>>> lower
>>>  DC resistance than a hot one.
>>>
>>>  So the initial turn-on current of the two bulbs together can be
>>> anywhere
>>>  between 18 to 36 amperes, but that surge will be brief - somewhere in
>>> the
>>>  tens to hundreds of milliseconds. Less than a second, anyway.
>>>
>>>  Clearly the steady-state current draw of the two bulbs (3.6A) is well
>>>  below the 13A current rating of the wire and the 8A fuse. The fuse can
>>>  handle the brief turn-on surge.
>>>
>>>  When I doubled the load by adding a pair of 21W trailer lights, the
>>> fuse
>>>  blew the moment I stepped on the brakes for the light test. Maybe
>>> because
>>>  the steady-state current (7.2W) exceeded the 8A rating of the fuse --
>>>  that's darn close (anyone know the tolerances on these cheap fuses?).
>>> More
>>>  likely, doubling the inrush current to somewhere in the range of 36 to
>>> 72
>>>  amperes popped the fuse.
>>>
>>>  But doubling the brake light loading doesn't exceed the current
>>> carrying
>>>  capacity of the wire. "Noxious smoke and fumes" are not likely to
>>> result
>>>  from passing 7.2A through wiring rated to 13A @ 60C insulation. The
>>> inrush
>>>  current of the bulbs is too brief to heat a length of wire 12 or more
>>> feet
>>>  long by more than a few degrees. It certainly won't "glow like a
>>> lightbulb
>>>  filament" even if I was passing 16A through it steady-state due to a
>>>  wiring fault. It would get darn warm and eventually the insulation
>>> would
>>>  fail somewhere.
>>>
>>>  Going from 3.6A to 7.2A in wiring very conservatively rated for 13A is
>>>  safe enough for me, especially since I only drive with the trailer a
>>> few
>>>  times a year. I reckon the engine will give out before the wiring will.
>>>
>>>  BUT -- Mike B. is right: DO NOT try this at home. Just because I jump
>>> off
>>>  a bridge doesn't mean you should. I do not need a phone call from your
>>>  widow's lawyer. Never modify any wiring or electrical accessories on
>>> your
>>>  van unless you know what you are doing and are willing to accept the
>>> risks
>>>  of a miscalculation.
>>>
>>>  --
>>>  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 5:16 PM Mike wrote:
>>>
>>>  > 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 <mailto:anasasi@GMAIL.COM>
>>>  >     *To:* vanagon@GERRY.VANAGON.COM
>>> <mailto: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 <mailto: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
>>> <mailto: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
>>>  >      >>
>>>  >      >>
>>>
>>