[Vwdiesel] Re: a meta-bentley question

[Brian or Pam Harrison]

Hi Shalyn;
The output from the "W" terminal is AC which has a changing
frequency proportional to engine rpms. The output is used in the oil
pressure warning system, the tachometer, the up-shift indicator
system and glow plug relay. I put a VDO diesel tach in a 1980
Rabbit diesel that I had one time. I took the alternator apart and
soldered a wire on one phase of the 3 phase AC generator before
the output goes through the diodes to be rectified into DC. I also did
the same thing to a couple of mid 80s GMC trucks with the 6.2 L
diesel so that they would have a tachometer. If is broken at the
alternator, it can be fixed.
You should check yours to see if there is an AC output at the "W"
terminal, the wire should be red with a black stripe and will go to the
fuse box  ( connector C, pin 11 ) where it is distributed to the other
items that use it. Check for continuity from your fuse box connector
back to the alternator to make sure there are no breaks in the wire.
Any wire that has that colour code should be part of that circuit and
should have the same voltage on it. That is the same colour wire
that goes to the tach in the instrument panel.
Regards;
Brian
Stewiacke, Nova Scotia, Canada
roseland at ns.sympatico.ca
"VW Diesel Driver Since 1978"
63 Type 2
72 Beetle
85 Jetta GL td 617,000km
95 Passat GLS td wagon 260,000km
97 Jetta GL TDI 140,000km
www3.ns.sympatico.ca/roseland



> Message: 3
> Date: Wed, 17 Jul 2002 21:08:44 -0500
> From: Shalyn Shourds <sshourds at flash.net>
> Organization: FlashNet User
> To: vwdiesel at vwfans.com
> Subject: [Vwdiesel] a meta-bentley question
>
>     Since this has come up....  I recently took the old '85
> Jetta TD on a 2861 mile trip across the southern US.
> Somewhere in Eastern Tennesee, the tachometer started
> dipping.  I pulled over and tightened the belts thinking it
> was the alternator belt slipping.  It wasn't.  Pulled over
> again and messed with the wires some and the tach totally
> died.  About the same time, when I checked inside the cab to
> see if the tach had come back to life, I saw that the "buy a
> new engine" (oil pressure) light and buzzer were in full
> force.  I eventually regained my courage and figured it was
> an electrical problem, jiggled the wire on the oil cooler
> sensor and it went away.  I still have no tachometer,
> though.  I looked into Bentley, but the wiring diagram stops
> at a black box.  Anyone know what kind of output I should be
> getting at the W terminal at idle--a steady voltage, some
> kind of alternating current?  Or, anyone know where the wire
> goes after it enters the firewall?
>
>         I appreciate any guidance.  The car runs fine, but I
> bothers me to see that tach needle dead on zero.  Car ran
> great on the
> rest of the trip.  Only creepy part was realizing I was the
> oldest car on the highway.  Even older than the cars on the
> side of the road.  I guess that's a good thing, though.
>
>         -Shalyn
>
>         '85 Jetta TD 270,000 mi.