gas gauge

[Bill Toppin]

I have not been able to get this thing to work. I changed the car to negative ground and had the gas gauge rebuilt. I installed a new sending unit. The wires have all been checked and they seem correct. When I turn on the car the gas gauge does not move,when I turn on the lights the gauge goes to full. Do I need to change my wires from the gas gauge for negative ground.
The car is a BT7 62.
thanks for any help. Bill

 

[Michael Oritt]

Bill--

The gas guage is not polarity sensitive but at the very least it sounds like you have some wires that are hooked up incorrectly. Perhaps your tank IS full and the light switch is somehow powering up the guage versus its being powered by the igniton switch?

In any case why don't you start solving the mystery by pulling the sender and, using an ohmmeter, see if the resistance changes from 0 to 90 ohms as you swing the arm through its limits.

BTW did the guage ever work properly and if so when did things change. Report back--we all love solving these mysteries!

 

[bighealeysource]

Hey Bill,
My gauge is still positive ground so can't address the negative ground issues but
had problems with mine until I grounded the sending unit to a chassis ground.
Simply ran a wire from one of the screws that hold the sending unit to the
tank opening and ran that to a chassis ground. Works now where before would
either real completely empty or completely full - of course that was because
I had the terminals in the back of the gauge connected backwards too !
Good luck,
Mike

 

[andybj8]

As Mike says, the unit makes its circuit thru being grounded, it does this thru the fuel pipe and fixings. Therefore if you have fitted any rubber pipe (fuel filter?) or plastic fuel clips it will struggle to make the circuit.

The tank is probably not touching any metal either (sitting on rubber square in floor opening) and being well painted, so the only path is thru the pipe or add a supplementary wire as Mike.

As Michael says they are not polarity sensative
And as Michael points out it seems like you are picking up the wrong supply and the gauge is being powered by the light circuit and will always therefore show full, are you sure on this? a bad ground will give a full reading.

Let us know if you are sure on the light circuit and we can study the circuit diagram (at work at moment so dont have one)



cheers Andy

 

[Bill Toppin]

thanks for the response.
I did try the new sinding unit (from Moss)before installing. All seemed to work properly.
so we checked gauge (newly restored by Nisonger Instruments in N.Y.)by running jumper wires with gauge both in and out of the car. I'm not sure how to test the gauge by itself.
Bill

 

[SideShifter Tri-Carb]

You can test to see if 'grounding' is the problem by taking a jumper wire with clips and ground the body of the sending unit to a chassis bolt.

 

[Bill Toppin]

I don't know why but I ran a new wire from the t pole on back of gauge to sending unit and it seems to be working. I still don't know why the old green w black s wire tested to be good . Thanks for all your ideas hope this works
Bill