Tom -
If the engine runs and shuts off with the key the white wire is ok. The white
wire is the only source of current for spark. Again, if you touch your probe to
the metal clip on the back of the tach you are not touching the white wire.
There is no connection between the white wire and the metal clip except a small
magnetic field caused by the loop in the white wire. If you were to puncture
the white wire with your probe at the back of the tach you will get the same
signal as you get at the coil.
Don't know what the sensitivity of the tach is but I would not chance testing
it with a current source. Could blow it out easily.
I recommend you take or send it to a speedometer shop to test and repair. These
speciality shops usually do pretty good work and are less costly than new.
Luck
Ernest
----------
From: tom.wagner@Central.Sun.COM (Tom Wagner - Program Manager)
Sent: Wednesday, June 19, 1996 12:36 PM
To: barrister@lawref.com
Subject: RE: Tach Help
Ernst:
Are you then saying that because my probe
is not at the coil, I can not tell whether
it is the wire or the tach device itself.
How can I be sure that the tach is the problem and
not something else, besides spending big $$$ for a
new tach.
Is there anyway for the tach can be cleaned
or do I just have to send it out and hope for the
best?????
Thanks
Tom
> From barrister@lawref.com Wed Jun 19 14:29 CDT 1996
> Date: Wed, 19 Jun 96 12:26:48 -0700
> From: Ernest Gilbert <barrister@lawref.com>
> Mime-Version: 1.0
> To: tom.wagner@Central (Tom Wagner - Program Manager)
> Cc: mgs@autox.team.net
> Subject: RE: Tach Help
> Content-Transfer-Encoding: 7bit
>
> Tom -
>
> Yes it is a straight wire from the loop on the tach to the coil with no other
>connections. The reason you can't get a signal at the metal clip on the tach
>is the inductivly coupled signal to the metal clip is too small. The tach is
>a current operated device. Resistance is very low and the voltage developed at
>that metal clip is very low. The analyzer input is a high resistance device
>which the low resistance of the tach effectively shorts out.
>
> Ernest
>
> ----------
> From: tom.wagner@Central.Sun.COM (Tom Wagner - Program Manager)
> Sent: Wednesday, June 19, 1996 11:05 AM
> To: barrister@lawref.com
> Subject: RE: Tach Help
>
> Ernst:
>
> I know about all of this, but what I have a problem
> with is not registering on the analyzer at the point
> of that loop. The loop as a metal point that attaches
> itself to the tach. I need to know is that a straight
> wire that goes back to the coil, or does it go somewhere
> else. I get no reading at the point that the loop
> is, but do get a reading at the coil connection.
>
> Any ideas????
>
> Thanks
>
> Tom
> > From barrister@lawref.com Wed Jun 19 12:01 CDT 1996
> > Date: Wed, 19 Jun 96 09:58:50 -0700
> > From: Ernest Gilbert <barrister@lawref.com>
> > Mime-Version: 1.0
> > To: tom.wagner@Central (Tom Wagner - Program Manager)
> > Subject: RE: Tach Help
> > Content-Transfer-Encoding: 7bit
> >
> > Tom -
> >
> > The white wire from the coil goes directly to the tach, loops around a
>pickup, and then to the ignition switch. There is actually no connection at
>the tach, only an inductive loop. The tack measures the current in the coil
>primary through this inductive loop.
> >
> > The white/black wire goes to the points in the distributor and through the
>points to ground.
> >
> > Hope this helps
> >
> > Ernest
> >
> > ----------
> > From: tom.wagner@Central.Sun.COM (Tom Wagner - Program Manager)
> > Sent: Wednesday, June 19, 1996 9:45 AM
> > To: mgs@autox.team.net
> > Subject: Tach Help
> >
> >
> >
> > I have a 67 B, and I need some help
> > on why my tach won't work. I know that
> > the engine analyzer works at the coil
> > okay, but when it is hooked up at the
> > tach, there is no reading. SO......
> > Can someone tell me the wiring from the
> > coil to the tach??? How the wires go and
> > what they go to. Some suggested that the
> > tach might be bad, but when the analyzer is
> > hooked up directly to the wire that goes into
> > the tach, this doesn't work either. The schematic
> > that I have is to good, as it is cryptic for
> > this old man. I know that the wire is white or
> > white w/black tracer.
> >
> > All help appreciated.
> >
> >
> > Thanks
> >
> > Tom Wagner
> >
> > `67' MGB
> > (Various stages of restoration - All
> > Paint removed to metal, working on rust
> > removal.) Waiting for day to become daily
> > vehicle.
> >
> > `92' Honda Civic LX(Excellent car)
> >
> > `93' Honda Civic CDX(Moms car)
> >
> > Sun Microsystems
> > Sun Service Division - Program Manager
> > Phone: 713-964-7068
> > Email: tom.w.wagner@Central.Sun.com
> >
> >
>
>
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