Hi Evangelos,
The needle moving the way you describe is usually caused by bad connections
in the green circuit - the extra load of other components is dragging down
the voltage. The turn signals I can understand, but I am a bit surprised
you mention the hazards as well, as this implies bad connections in the
brown circuit (the hazards come direct off the brown, the turns via brown,
ignition switch, white, fuse and green).
Did you measure the voltages while the turn or hazards were flashing? There
will always be some volt-drop while this is happening but it shouldn't be
more than, say, half a volt. If it is more than a volt then you need to
check the voltage back through the above circuit. If you can find two
points where it varies significantly more at one than the other, then the
problem is between the two points. Bear in mind you could have more than
one bad connection in the circuit. If the voltage reads good at the tach
but it is still dancing in tune with the turns, then I am at a bit of a loss
as to what to suggest next, short of using an oscilloscope and looking for
voltage spikes and troughs.
Good luck,
PaulH.
----- Original Message -----
From: Evangelos G. Makris <xirias@hol.gr>
To: <paul.hunt1@virgin.net>
Cc: <mgs@autox.team.net>
Sent: Wednesday, August 09, 2000 7:10 AM
Subject: Re: Tach is dead
> Paul,
> The tachometer on my car (73 GT) won't register above 3,000 rpm even if I
rev
> the engine above that. The needle dances when I switch on the indicators
or
> hazards to the rhythm of the flasher unit(s). I measured current coming to
the
> unit with an analogue multimeter and it was as you described. I gave it a
tap
> with my hand but nothing changed. Would you say the gauge is at fault?
>
> Regards,
> Evangelos
>
>
> paul.hunt1@virgin.net wrote:
>
> > OK, then you should have 12v on the green, ground on the black (a wiring
tag
> > secured under one of the knurled nuts that clamp the tach onto the dash)
and
> > the white/black should be switching between 12v and ground when the
engine
> > is running. Note that an analogue meter will display this last as about
6v
> > and a digital meter may not display a settled reading at all. If you
have
> > an after-market electronic ignition system you may get different
readings on
> > the white/black, and this can be the cause of the tach not working
anyway.
> >
> > If you have these readings on the back of the tach the wiring is OK and
the
> > tach itself is suspect. By the way, seeing as how the car has not run
for a
> > couple of years it could be stuck. Have you tried giving the tach a rap
> > with your knuckle while the engine is running? If the needle bounces
off
> > the end stop but still does not register then the problem is possibly
> > electrical inside the tach and not mechanical. If it stays on the end
stop
> > it could be well stuck.
> >
> > PaulH.
>
>
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