Dave writes:

OK...a 1976 PA 28 151..

After a few minutes of running, the port guage will start to fall
towards E.
....
Shut down for a few hours, guage resumes normal (correct) indication.

We have checked / replaced, tank grounds, sender, wiring to guage.

What about engine grounds? Battery grounds?


I think the guage terminals handle 12 V to the left terminal
(looking at it from under the panel) (starboard terminal) , The other
to the tank sender (port terminal).. (grounding this terminal when
the fault is present will cause a "full" indication).

From what I recall, there is a "ground" connection internal in the
guage. Anybody know how this is grounded?

I suspect a bad connection here somewhere..

Well, that's a fair guess. Especially since it looks like
the sender resistor is "0 ohms == full; many ohms == empty"...

Driving me up the wall..of course every time I attack the problem,
meter in hand, it works fine.

Tape a spare DVM under the panel, near the gauge. This threat should scare
it into working....

But let's do an obvious test. Can you swap the leads to the two
tanks; so the left shows on the right gauge and vice versa? [Assuming
such can be done legally and safely, of course -- can you placard
it or such?]

That will reduce it to gauge vs sender resistor+wiring+grounds.


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