I want to second this.  Mark D's "tool" should be carried in everyones kit.
 I built one last summer after I bought a non-running parts van.  According
to the PO, it had a rebuilt engine but "something screwed up electrically.
 We couldn't get it started."
  With this basic harness and a remote starter switch I got it going and
verified that the engine and transmission are usable to transplant into a
Westy that needs them.
   I made one modification to the design.  I skipped the long wire from the
battery and just used a shorter lead with an alligator clip to hook to the
positive terminal on the alternator.  I figured that a fault between there
and the battery would be easy enough to detect and fix.  Maybe
crazyvwvanman will let me know why this was not a good idea.    :-)

Larry A.

On Fri, Apr 25, 2014 at 12:00 AM, Mark A Kippert <vanagon@kippert.com>wrote:

> Just wanted to take a minute a post about a great diagnostic tool I
> discovered on The Samba a few years ago. I've probably posted about it
> before but it's worth mentioning again.
>
> <
> http://www.thesamba.com/vw/forum/viewtopic.php?t=349429&postdays=0&postorder=asc&start=0
> >
>
> While driving home one day my van started bucking and jerking like someone
> was toggling a switch. I barely made it home. Soon after my van refused to
> start at all. The starter cranked just fine but nothing from the engine.
>
> At this point I did what most people do, pop the hood, or engine cover in
> this case, and stare mindlessly at the engine hoping the solution would
> just pop into my head, which, it kinda did. I remembered about a year
> before building this diagnostic tool for another no-start issue. So I
> hooked it up, per instructions, and vroom, the engine purred to life! At
> that point I started disconnecting the three leads one at a time (again,
> following instructions).
>
> First lead I removed was to the coil. Fired right up. Second was the lead
> to the ECU relay. Nothing. Cool, we're getting somewhere! Hooked it back up
> and disconnected the lead to the fuel pump. Fired right up. So, I
> determined that the issue lies with the wiring related to the ECU relay.
>
> After consulting the Bentley wiring diagram (ouch, my brain hurts) I
> determine what wires go where. First I probe the hot lead (red wire, always
> hot) going to the relay. It's hot as it should be. Next I check the black
> lead that activates the relay when the key is turned on. Nothing. According
> to Bentley, this wire comes from the coil. I start probing the wire at
> several points. Nothing. I determined that the connection at the coil is
> hot (with key on) so it has to be the push-on connector itself. I break
> away the plastic shield from the connector and find it to be green and
> corroded. Not too surprising on an old Vanagon. I snip the old connector
> off and crimp on a new one. Vrooooom, the engine comes to life! Sweet!
>
> The credit for this great tool goes to crazyvwvanman (Mark) on The Samba.
> Thanks!
>
> Mark K
> 1986 GL/2WD/4SPD "Abe"
> 1991 GL/2WD/4SPD "project"
>