Fuel Sender Earth?
 

I've been trying to work out why my fuel sender isn't working (shows below empty all the time). I'm starting to think the earth wire with the rubber plug on the end needs to go onto the top of the sender unit rather than the tank itself?

No one able to help on this one? If it helps the gauge goes to below empty as soon as the ignition is turned on and then when switched off, it slowly creeps back up to 1/4 of a tank?

is the sender matched to the guage? they have to match to work.

failing that you should have 2 connections usually on the sender

an earth
and a signal wire to the gauge

the gauge should have 3 wires usually

an earth
a signal wire from the sender
and a 12v power supply

[maybe a 2 more for a background light]

if your not getting correct readings i would first check the sender is matched to the gauge. if thats ok it will probably be the earth not making contact. try getting a spare bit of wire - bare both ends - then put one end on the earth connection on the sender the other to a good earth point on the chassis. see if gauge moves. if it does the earth wire already there is not working.

also make sure the float inside the tank has full range of movement - take it out [but still with wires connected] turn power on and move the float arm manually - see what happens to the gauge. is it back to front? or is it catching the tank - bend it to suit [if it has a wire type arm]

ideally you would like it to just skim the bottom of the tank when the float is on the lower stops [be hard to see but it is possible - you dont want the float to hit the bottom first or the gauge will read some left when there isnt]

be very meticulous with your wiring - find each wire in the circuit and check its good - bet you find one thats slightly loose

Its the original sierra sender & gauge I'm trying to use from a 1993 injection sierra. I'm sure it has 3 wires going into the sender though, a red, brown and green one. Like you said odds are the problem is my earths so I'll have to check where the earth for the instrument cluster as that might be my problem.

If it is anything like gus's fuel sender was you should have two wires going to the sender. One was brown/black which pushes onto a bolt sticking out of the sender. The other wire was brown which pushed onto a metal stup which is part of the sender cap.

You should also provide an additional tank earth strap to the chassis.

I had a play with this last night and for whatever reason the sender needs the brown earth wire that goes into the loom (same earth point for the pump) attached to the top of the sender. The plate I have the sender attached to which will sit on top of the tank also has to be touching the metal on the tank to earth it I guess for the gauge to work.