1959 Cadillac gas / fuel tank sending unit

[kib]

What can it be Doc 

My fuel tank sending unit show a little movement when I turn on the ignition, when I turn on the light it suddenly show full tank.
What may this bee?

T.Kibsgaard

[waterzap]

Not familiar with this particular unit, but other sending units I have played around with, as the float moves up and down, it changes resistance in some form of potentiometer. When the float was at the bottom, the resistance was around 5 ohm, at the top (full tank) around 100 ohm. My guess would be if you break a wire in the circuit, it will show 100 plus ohm (actually infinity). Fuel gauge thinks the tank is full. Some way, when you turn the light on, the resistance goes up. Might have to take the sending unit out of the tank and start there.

[J. Gomez]

Thore,

It could well be cross wires at the terminal plug, or some type of cross at the panel foil traces.

The “brown” on the right side terminal pin 6 would be from the fuel sender to the fuel gauge the other side of the gauge should have a switched (ignition switch) +12V (most likely “pink w/black stripe”).

The pink/black would also supply power to the temp gauge, is your temp gauge working?

If

Good luck..!

[kib]

Hi,

Is this deschribed on the wire drawing? My temp gauge is showing just a little temp, meaning I can se a small movement when turning on the ignition. Same movement as on the fuel sender.

Thore

[J. Gomez]

Thore,

Yes the wiring diagram shows the temp and fuel sending units up to the right and left side connectors up to the panel. You can see the wiring diagrams at;

Left side
http://www.oldcarmanualproject.com/tOCMP/wiring/5765wiring%20diagrams/Cadillac/MWireCadi65_3WD-038.jpg

Right side
http://www.oldcarmanualproject.com/tOCMP/wiring/5765wiring%20diagrams/Cadillac/MWireCadi65_3WD-039.jpg

However these drawings do not extend up to the back of the cluster panel. I trace in red on the picture attached the switched +12v side to both gauges.

Hope this helps.

Good luck…!