[T3] Fuel gauge issues (jumpy needle)

[Jacob Adam Schroeder]

I suspect it is a ground issue, but I am less certain of how to confirm
that is the case.  I guess I am having trouble understanding where the 1972
fuel gauge circuit is supposed to ground.  It appears as though a signal is
sent from the gauge through the sending unit and that the sending unit
grounds to the body through the tank.  Is that correct?  Are there any
other grounds?

On Thu, May 28, 2015 at 6:23 PM, Craigs List <craigslistcsprings at gmail.com>
wrote:

> Have you checked that is is properly grounded? A bad ground can cause a
> jumpy needle. I have one myself.
>
> Adam
>
> On Thu, May 28, 2015 at 6:00 PM, Jacob Adam Schroeder <
> jacob.schroeder at gmail.com> wrote:
>
> > Also, I saw the fix that somebody shared previously about drilling a hole
> > in the center of the sender.  That was interesting but I'd prefer not to
> > make that mod if I can avoid it.
> >
> > On Thu, May 28, 2015 at 3:58 PM, Jacob Adam Schroeder <
> > jacob.schroeder at gmail.com> wrote:
> >
> > > I have a 1972 Squareback and have been having a recent issue with my
> fuel
> > > gauge.  I recall the the gauge used to work, so I am not sure what has
> > > changed over time.
> > >
> > > The gauge appears to be accurate, when it is steady.  But the problem I
> > > have is that the needle jumps around like crazy (especially when I am
> > > driving).  From looking at the gauge, it appears that there are two
> > ground
> > > points: (1) through the housing to the spring clips to the dash, and
> (2)
> > a
> > > ground wire to the back of the gauge through the black plastic piece
> that
> > > clips on to the rear of the gauge.
> > >
> > > Are these grounds redundant in that only one has to be good?  Do both
> > > grounds service the fuel gauge or is the wire for the lights and the
> fuel
> > > gauge grounds through the clips?
> > >
> > > The bouncing needle to me indicates a grounding problem, but I cannot
> > seem
> > > to track it down.
> > >
> > > Also, I followed the test in Bentley--disconnecting the sender and
> > > grounding the wire to the sender housing, and the gauge reads full.
> So,
> > > according to Bentley, the sender is good.  I tested a spare sender and
> > get
> > > the same jumpy needle.  So I am fairly confident my sender is OK.  But,
> > do
> > > the late (1972) sending units need a tab of exposed metal on the tank
> for
> > > grounding?  I saw something to that effect in Bentley and I did repaint
> > my
> > > tank within the past few years, but did not leave a portion of exposed
> > > metal along the circumference of where the sending unit mounts to the
> > tank.
> > >
> > > Also, could be unrelated, but I also get an intermittent fast turn
> signal
> > > blink that may share a similar cause.
> > >
> > > Any help would be appreciated.  Thanks,
> > >
> > > Jacob
> > >
> > >
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