At 07:57 AM 3/15/2004, fastvanagon wrote:
>If possible, I need these measurements done with a digital meter.
>With the "T14" connector unplugged, start the Vanagon and do a
>voltage measurement across pin number 3 and pin number 9.  Again, do
>the same for the current measurement.  Verify that the meter is set
>to the proper 12VDC setting for the voltage.  Verify that the meter
>is set to the proper DC current measurement.  If you are unsure of
>these meter settings or pin locations, please do not attempt.

Erm...I'd suggest not doing this, and in particular not doing the current
measurement.  In the '87 and all other watercooled Vanagons, the tach drive
is connected directly to the ignition coil drive signal.  If you don't
believe me you can do a continuity check between the panel connector and
the dual terminal on the ignition coil -- or just lick your finger and put
it on the connector on the back of the tach while the engine is
running.  Try not to be driving when you do this, it upsets the other
drivers.  Or of course you could look at the wiring diagram...

Voltage measurements will only be accurate if you use an oscilloscope (I
suspect something like 200 volts peak, and if you really need it I can
measure it on my '84).  This is not enough to pop the input stage of your
average meter, but it's a consideration you should bear in mind.  The meter
*will* give you the average voltage with a fudge factor to read as RMS or
"effective" voltage -- but the fudge factor assumes a sine wave and not a
pulse train, so unless you're using a meter with true RMS readings it won't
be accurate.  Someone on this list (Mark Drillock?) knows whether the tach
counts pulses or simply integrates the input signal the way a digital meter
does -- I suspect the former.

Measuring current from this signal to ground is equivalent to shorting the
coil drive to ground through the shunt resistance of the meter.  Shorting
the output stage of transistor devices is seldom a good idea because the
transistor can destroy itself in the blink of an eye from
overcurrent.  "Transistors fused against the worst -- protect the fuse by
blowing first..."  In the case of the 2.1l Digifant, that transistor is
located inside the ECU.

david

--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"