At 10:34 PM 3/6/99 -0800, you wrote:
>I tried grounding the sending unit and grounding the tank. Seems strange
>that the sending unit appears to be inuslated from where the wire connects
>on the top, although checking with the ohm meter, there is continuity from
>the terminal to any part of the sending unit. Could this be a problem?
>
>Smokey
Smokey
I think the wire hooks to the top end of the potentiometer that the float
controls. The bottom end of the potentiometer is ground thus they have to
insulate the wire or the pot would be shorted out.
As for why the thing doesn't work, well that is a puzzler to me too. I'm
not sure if I have all the details correct but you have a electrical system
that has been converted to 12 volts and you are trying to use the original
6 volt gauge and sending unit. Correct?
I am wondering if the sender you installed was for a 12 V, rather than 6V,
system.
For instance lets suppose that at half tank the sender potentiometer reads
30 ohm (made up numbers, I have no idea what the resistance of the pot
actually is). If you have a 12V system by Ohms Law the current flowing
through that circuit is
Current(amps) = Voltage(VDC)/Resistance(ohms)
so
Current = 12/30 = .4A or 400 milliamps
Which, lets say for the sake of argument, is what it takes to move that
gauge needle over 1/2 way.
Now lets say you reduce the voltage down to 6 VDC (with the same sending
conditions)
you have
Current = 6/30 = .2A or 200 milliamps
That's only half the current and it may not be enough to overcome the
static condition of the gauge movement and make it register.
I guess what I'm saying is, is it possible the sender is designed for a 12V
system? Maybe there are two different units?
It would seem to me that you could check this by removing the reducer and
applying 12V to the IGN terminal on the gauge, (just for a split second in
case I'm full of sh*t) and see if the gauge comes to life.
Again I've never really fooled with one of these things and I'm not
familiar at all with the electricals of an AD truck so I might be full of
it. :)
Good luck!
Bill
Bill Bailey
57 Chevy 3100
http://members.tripod.com/~oltruck
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
|