Digital Dash

[Ivan141]

I really have no idea why (and indeed if) the digital gauge needs this fuel signal for the tach to work, but if it does the above schematic is not ideal.
On the analog fuel sender (which should be similar to the digital one except for its resistance range) fuel sender ground splits off into a thermistor for level warning, and a rheostat for level measurement.

Applying that logic to this schematic I would say it is better to have a wire coming from pin 12, splitting off into a resistor to pin 5 and a resistor to pin 13.
As for resistor values: The low level warning probably triggers when resistance goes higher (due to higher temperature when it looses cooling from the surrounding fuel), so 180 is probably a good value to use.

I found the following suggested range for the level sender:
Full = 270 Ohms
Empty = 17-33 Ohms,

If that's correct 120 ohms would put you right about half full.

SO... why doesnt this work for you? Here's a possible explanation (wouldnt be surprised if it turns out to be wrong):

I expect the cluster is putting out about 12V on both pins 13 and 5 with nothing connected. If you now put that 120 ohm resistor across 13 and 5 like in the drawing, pin 13 will still be seeing 12 volts, so basically it's almost as if you haven't connected anything to pin 13.