[T3] Fuel gauge issues (jumpy needle)

[Jacob Adam Schroeder]

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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