On Friday, in article
> ""David G. Bell"" <firstname.lastname@example.org> wrote in message
> > Does anyone know the voltage that the Series III fuel sender should be
> > getting from the regulator?
> > I'm running a Lightweight, and as far as I can tell the actual sender is
> > the same. The voltage applied I measure at about 4.5 volts on the
> > disconnected lead, which seems low to me. The manual changeover switch
> > seems to be working.
> > This would suggest the fault is further up the chain, either the actual
> > gauge or the voltage regulator (it's a 12-volt system).
> I assume your fuel gauge isn't working from this. Are you trying to measure
> the output from the fuel gauge supply regulator or the lead to the tank
> unit? The regulator (on the back of the speedometer) keeps the supply
> constant so the gauge reads the same as the battery voltage fluctuates ( e.g
> charging after start up) and supplies a regulated 12 volts but the voltage
> (and current ) to the tank unit are very small ( I don't think you really
> want to put 12 volts in the tank for obvious reasons) and any dirty
> connections etc. will consequently affect the reading of the gauge. Check if
> the gauge moves when earthing the tank unit lead to the chassis as the most
> common fault seems to be corrosion at the tank mountings and not completing
> the circuit.
Thanks. Yes, I was reading from the lead to the tank sender, while
disconnected from the sender. And the other meter lead to a good contact
on the chassis. Bother, don't have an impedance figure for the meter to
hand, but 4.5v certainly implies a pretty huge resistance for the gauge
and wiring downstream of the regulator, dropping 7.5v -- I rather doubt
that a 1960s fuel gauge would have a useful response to currents
measured in microamperes.
I'll check tank-to-chassis. Since I'm getting a voltage, the fuse hasn't
blown, but check the contacts there...
David G. Bell -- SF Fan, Filker, and Punslinger.
"I am Number Two," said Penfold. "You are Number Six."