fuel gauge issue

[keri]

hi all I have a 1975 xjs and I noticed the fuel gauge did not operate at all also the fuel warning light was on so I assumed it was very low so added £40 light went out but gauge reads empty so removed sender there are 3 wires black earth and brown which is live with ignition on for the low fuel light and a orange/green wire to gauge also live with ign on so if I earth brown low fuel light is on this seems ok when I earth the green/orange wire the gauge goes to max full this I assume is ok but I have nothing in between even though with a multimeter over the black earth and orange/green connector on sender and operate sender I have a resistance so I changed the sender with a brand new one just in case but it is exactly the same it seems the gauge is a magnet in a magnetic field and 3 coils with 12v to one side and earth to other side of magnet and earth to sender so as resistance changes current flow to the coil is changed the magnet moves the gauge this is how it seems to work but mine does not could it be the gauge? any help many thanks does anyone have some clocks thanks
keri

[ptjs1]

Hi keri,

Not sure I can help much other than to say that your tests would seem to imply that the gauge, light and wiring loom are ok. The implication seems to be that the float or sender are thus at fault.

Good luck

Paul

[PaulGover]

I read somewhere that the float often gets fuel inside it through a pinhole, and that leads to under-reporting the fuel level. Don't know if that helps.

[keri]

hi all looks lik I will explain what I found just in case somebody has the same issue I found the culprit to my non functioning fuel gauge.
this what I found I removed the clocks to swap the fuel gauge with the temp gauge to test gauge and when I removed the 3 screws that hold the gauge in I found the center screw shorter than the outer 2 so removed the temp gauge but all 3 screws were the same length long like the outer ones when I looked at the gauge I could see that the screws that holds the gauge to the plastic combination meter body also go through and partially thread into a copper strip on the back of the gauge making contact between the gauge and printed circuit ribbon but the center screw was slightly too short and not quite making contact so found a longer screw and fixed it in so it made contact and the fuel gauge is working fine so just in case please check this also if you want to check your fuel sender without multimeter just remove it and the take it to engine bay remove the single temp sender wire on the front of bank a and connect it to the sender terminal that he orange/green wire would have been switch on ign and operate sender and the temp gauge should move up/down a quick and simple test to eliminate a sender fault also note that earthing the brown wire at the sender will put on fuel warning light that's ok but the green/orange wire to gauge if you earth this the gauge reads full and this is ok I have read that this confirms the gauge is ok but be aware this worked as explaind on mine yet the gauge did not work correct it seems when it is empty it earths on the sender body light on and vice versa when full earths on sender body reads full so the resistor does not work in both these positions which is why mine did not work operating the float because it was changing resistance in the earth return wire but no contact to gauge as the screw was too short hope this helps somebody
thanks all.