Why aren't I laughing?

[vincereynard]

I have had trouble with the fuel gauge not registering. I was advised to connected the feed to earth and - bingo - full fuel. Therefore the sender must have failed?

New sender fitted - nothing. Low fuel light on even though it has at least 2 gallons in there.
Both senders work fine - outside the fuel tank. Neither work when fitted.

The only possibility that I can think of is that the senders are the wrong length and are physically touching the opposite side of the tank and being held down - hence the low fuel warning.
But both fuel senders are the same (I think?) and I distinctly remember the gauge initially reading half full and then filling the tank to the max.

Now there's a funny thing!

[john.p.clegg]

Reverse the wires...fuel gauge,,low fuel.

John

[vincereynard]

Reverse the wires...fuel gauge,,low fuel.

John

I tried that, it simply went to full.

[Spyder fan]

Check the earth wire = disconnect it and run a separate cable from the negative terminal of the battery to the earth tag on the sender. Takes 2 minutes and removes that doubt from the equation.

I can't remember if it's possible to fit the sender upside down, but that would explain your low fuel light if everything is working correctly apart from your brain

[vincereynard]

Check the earth wire = disconnect it and run a separate cable from the negative terminal of the battery to the earth tag on the sender. Takes 2 minutes and removes that doubt from the equation.

I tried that a direct link from battery neg to sender with and without normal connection. It made no difference. And of course they work fine outside the tank.

I can't remember if it's possible to fit the sender upside down, but that would explain your low fuel light if everything is working correctly apart from your brain

It would be possible but they are marked T for Top.

I've had another case of arachnophobia - it would appear that the usual suspects put the throttle return spring on the wrong way round. Open the throttle past half and the throttle can stick, the cable slips out and the little barrel goes walk about. With luck no throttle connection, without luck half open carbs and no throttle connection. What fun.

[KevJ+2]

I'm probably way off, but could it be the voltage stabilizer? If it's okay off the car, the voltage supply on the car should be from the stabilizer. Is that correct

[vincereynard]

I'm probably way off, but could it be the voltage stabilizer? If it's okay off the car, the voltage supply on the car should be from the stabilizer. Is that correct

That's the mystery Kev. It is not "off" the car, its still using the same connections.
Waggle the float about and the fuel gauge responds. Full droop, the float arm touched the sender body, and the low fuel light comes on.

Just not when fitted into the tank! Bizarre.

[Orsom Weels]

If both sender units are the same, it would follow that if one were fouling on the tank side, or a baffle, then so would the other, I would be checking this out. Bend up a length of welding rod or similar to the same dimensions as the float arm, ie 90 degree bend to make an 'L' shape, make the foot of the 'L' the same length as the float, then measure from the mounting flange to the float (furthest side of float) & mark this dimension on the leg of the 'L', insert in to the tank to your mark, perhaps add a 1/4 inch to make sure adequate clearance, then move through an arc, mimicking what the float arm would do with the rise & fall of fuel. If there is something preventing free movement, you should be able to detect it, then work out what needs to be changed to clear the obstruction.
Also make sure the float arm is reaching the bottom of the tank on full drop, not hanging up on the sender unit stop, my friends series 3 had this problem, it needed a good 2 gallons of fuel before the gauge registered anything, then when full, it only registered 3/4. A bit of judicious bending soon had that rectified . Probably not your issue, as you say you have filled the tank, but worth a look while you're in there.
If it all works outside the tank, you have pretty much ruled anything else out

Tim