View source for Solving wiring diagrams -- a technique

David Bierl:

In understanding Vanagon (or any other) wiring diagrams there is a
not-so-little trick that will make it vastly easier to figure out
what's really going on in a circuit.  Before you can do this of
course you have to be familiar with Bentley 97.3-97.6. so the
diagrams make any sense at all.

The trick is this:  First copy the page in question (an enlarged copy can be helpful
because the wires are quite close together in the original pictures) so you won't
wreck the original if you mess up somewhere.  Get yourself an
assortment of colored pencils/markers, at least five or six including brown
and red.  Then take a look at
http://picasaweb.google.com/dbeierl/FiguringOutVanagonWiringDiagrams#
for a working example of how it's done.  You may want to keep it open
to refer to or make a color print of it to use the first time or two
you do this.

Start by locating the grounds.  Since this is a physical schematic
some of them may originate far away from where you're looking even if
it would be easier to understand if they simply drew all of them
straight down to line at the bottom line of the page, which is
chassis ground.  Every terminal labeled as 31 is a ground.  Every
ground you find, draw  a brown line next to the wiring for its whole
length. For switched grounds I recommend a dashed line instead of
solid upstream of the switch.

Then look for the +12 supply wires and color them red.  You may well
want to use different colors for unswitched (terminal 30), switched
by ignition (terminal 15),  and switched by the load reduction relay
(X-terminal on ignition switch operates it; power upstream is 30 at
the relay, downstream (switched) is 87 like all relay
outputs.  Again, power that's switched downstream should use a dashed
line downstream of the switch.

Now pick a wire and figure out what it does.  Follow it off the page
if necessary and label where it goes on your drawing.  If you can't
figure it out, pick another wire.  As soon as you know what it does,
label it as such then pick a color for it and draw solid or dashed
line as appropriate.  If a single wire does multiple things, as in
the circuit from 53e at the motor up to the switch, down to the relay
and thence to the motor 53 terminal, use multiple solid or dashed
lines as appropriate (Note: the pink wire should be dotted for its
entire length and there should also be a brown dotted line for the
whole length of that circuit.  Can you discover why?  Answers on
request.  Hint: I missed one of the functions of the auto-park switch).

Keep on doing this for wire after wire until you understand them all
(or are certain you understand enough of them, which may or may not
be true).  Each wire you figure out makes the rest easier, and the
colored lines take away the visual anonymity of Joe Random
Black-line-on-the-page.  Now you can follow the circuit around and
find out where a particular problem might (or must) lie as well as
where it cannot.

This is the second time I figured out this particular wiper
circuit.  The first time I forgot this trick I learned thirty years
ago, and it took me over an hour.  This time I remembered, and it
took about ten minutes after I found the colored pencils and
photographed the page.  And I was easily (but not in ten minutes)
able to establish that the relay cannot possibly be correct as drawn
(since at some point it would hook +12 directly to ground) and how it
would actually have to be (which happens to coincide with the diagram
molded into the side of the actual 19 relay, but I didn't know that
at the time.  I definitely did *not* figure that part out the other time.

Adds Roger:  "Once you learn these diagrams, you can troubleshoot any circuit easily, or do a conversion. Many of the color codes for Vanagon are the same for Jetta , Golf etc."

Originally posted on the vanagon mailing list by David Beierl with additions from response by Robert Keezer


[[Category:diagnostic_tips]][[category:understanding_bentley]]