66 fuel gage circuit

[Richard E.]

I'm looking to determine if the fuel gage, the sender, the harness or a combination of these are faulty. The fuel gage is stuck at about 3/4 full regardless if the engine is running or not (ignition on or off with the tank less than 1/4 full of fuel).

Can the fuel gage be tested (using a volt-ohm meter for example) from the wire harness connections at the tank sending unit? I'm trying to determine if the fuel gage is bad without removing the gage or dash cluster. I'm wondering if any fuel gage checks can be made at the wires connected to the tank sending unit if the wires are disconnected from the sending unit.

Also what voltage should be measured at the sending unit wires?(with the sending unit disconnected)

Can a fixed resistance (like a 45 ohm resistor) be placed across the disconnected sender wires at the tank end to simulate a 50% gage level reading for example? (Trying to determine if the sender is bad)

Appreciate any troubleshooting hints. I have a volt-ohm meter and access to fixed resistors for testing. Thanks much.

[Jim D.]

Re: 66 fuel gage circuit

http://www.lbfun.com/warehouse/tech_...rFuelGauge.pdf

[Gary C.]

Re: 66 fuel gage circuit

Hi Richard,
This article should help you.

http://www.lbfun.com/warehouse/tech_...rFuelGauge.pdf

Cheers,
Gary

[Richard E.]

Re: 66 fuel gage circuit

Thanks much Jim & Gary this information will definitely help.

[John H.]

Re: 66 fuel gage circuit

Richard -

Here are the two circuit diagrams that go with my article.

C1/C3 Fuel Gauge System:



C2 Fuel Gauge System:

[Richard E.]

Re: 66 fuel gage circuit

John,
Thank you very much for the sketches, this is a significant help. I forgot to mention also that the battery meter (ammeter) needle lays to the far left (-10 position if I recall) with the battery connected or disconnected and regardless whether the ignition switch is on or off or engine is running. The alternator is charging, this was checked with a test volt meter.

I expect this means the battery gage needs to be replaced. It appears there is no link between the battery gage and fuel gage circuits.
Thanks again.
Regards,
Rich

[Ronald L.]

Re: 66 fuel gage circuit

Richard, look for some threads on this same subject from March April where I identified the senders themselves --NEW--- as not having the specified resistance of 90 ohms. Once I got one that read '90 at full' my issues were solved, and since it appears the ground side of the sender coil was the fault point, erratic reading on other items were no longer a problem once I isolated that ground.