Hi I have a problem when I turn the key on in my 64 convertible, the fuelgauge goes up to half full (and I know there is half a tank of petrol) then after a few seconds it goes back to empty. I am thinking it may be a problem with the sender unit. Also when I put a test light on the wire to the sender unit at the fuel tank the charge to the wirepulses rather than the light stays on is that correct and has any one had the same problem.

 

I would check for a break in the wire, possibly rubbing on something/shorting out.

 

There is no power to the sending unit. It grounds the gage to the chassis. To test it pull the wire out of the sending unit and ground it, it should read full. So you may have a bad wire or the tank is not being grounded properly, from rust...

 

Completely new floor and tank is screwed in with steel screws hopefuly that covers the grounding issue. I forgot to mention this has just started happerning was working ok up until aweek ago? Might try going down the bad wireing track

 

There is power to the sending unit but it is regulated low voltage.
The pulsing test light is caused by the constant voltage regulator(CVR). This would be normal.
If the other water temp gauge is working correct then the CVR is probably good and the problem is something else.

 

Thank you 65 Coupester that is very helpful. So if I remove the sender unit from the tank is there any way of checking for faults i.e. use a volt meter and how would you check to see it floats ok.

 

Yes, you can check the fuel sender with an Ohm meter. It should read between 25 Ohms and about 250.
With the sender out of the car put the Ohm meter leads on the sender connector and the flat plate it is all mounted on. Move the arm the float is attached to.

The check the float, just shake it. If it is full of gas, it has sunk.
Or just stick it in some water and look for bubbles.

 

Cool thanks for that you have been a great help.
I live in New Zealand and finding some one you knows is hard to come buy. Cheers.