> A couple of years ago, I had a new outboard motor installed on my
> old power boat.  The installation included an instrument panel, and
> said panel included a fuel gauge.  It was never hooked up, however
> -- merely a standard thing that was included.
>
> The other day, I had to have a leak repaired in the fuel tank, and I
> asked the guy to put in a new sending unit and hook it up to the fuel
> gauge for me.   I picked the boat up today, and the fuel gauge does
> not budge, although the tank is about 3/4 full.
>
> How would I go about trouble shooting the fuel gauge?  The sending
> unit itself is merely a float inside the tank, with a wire going to
> the gauge, isn't it?  I would assume that as the float moves up or
> down, there is a varying resistance.  And I would assume that the
> fuel gauge itself is merely an amp meter with the current varying as
> the resistance of the sending unit changes.

That's the general theory of operation.

> I further assume that one side of the meter would go to ground, while
> the other side would be hot (going through the resistance).  So the
> whole thing should be able to be checked, using merely a multimeter.

I think one side of the meter goes to hot (through a fuse).  Other
side of the meter goes to the float sender.  Easier to wire since you
only need 1 wire from gauge to sender.  Other side of sender goes to
ground (usually via metal fuel tank).  This also minimizes probability
that a wiring short would allow full voltage/current to heat up the
sender (submerged in gasoline).

Is the fuel gauge hooked up backwards?  Can you get a part number off
of the fuel gauge and find a datasheet for it?

Have you hooked up a dummy load (i.e. potentiometer) in place of the
sender and seen if the fuel gauge will move as you adjust the pot?

                                                Lee Jones

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