Resistance of sending unit for fuel guage

Tom in TN · Oct 1, 2015

I bought a 1963 Ford 4000 diesel. The lights don't work and the fuel gauge doesn't work. I know a fair bit about electricity and am in the process of fixing those items.

I measured the resistance of the fuel gauge and of the sending unit. The fuel gauge itself is 192 ohms. I think that's way too high. I think it should be a couple of ohms. The fuel tank is about half full, and the resistance of the sending unit is 100 ohms.

What do you think? Are both of those about right? One of them about right? Neither about right.

I think the sending unit is okay but the gauge itself is shot. What do you think?

Tom in TN

Dean · Oct 2, 2015

I have some old 6V units around here somewhere from similar gasoline tractors but do not know resistance values.

Firstly, I would verify that the sending unit is properly grounded to the fuel tank. Most are not.

Secondly, I would verify that the brass float has no damage. If it has been out of adjustment, the float can rest on the bottom of the tank resulting in vibration induced perforation.

Be advised that the readily available aftermarket gauges/sending units are not compatible with OEM units. If you change one, you will need to change both.

Dean

Tom in TN · Oct 2, 2015

Dean,

Thanks for the response. New Holland has a replacement gauge available for $65.00. I'm leaning toward replacing it first. I haven't pulled the sending unit out of the tank yet because I didn't want to disturb the seal unless I had to.

I'll check the mounting of the fuel tank to make sure that it has a good, clean ground connection.

Mine is a 12 volt, 4 cylinder diesel tractor.

Tom in TN

Hobo,NC · Oct 2, 2015

Can you reach the sender with a wire, if so pull it up to the top record resistance, lower it to empty record Resistance with a analog ohm meter... Note disconnect the gauge from the sender...

The only record I have for a older ford of any kind car/truck are tractor

Low- 76 ohms
Mid point- 23 ohms
High 9 ohms

I have never checked gauge resistance I never seen a reason 2...
I don't know if they used a voltage regulator/switch in your set up..

Tom in TN · Oct 2, 2015

Thanks Hobo,

I never thought to try to "fish" for the float through the gas cap. I'll try that tomorrow and see what I get.

I destroyed my last analog meter a couple of years ago, but I have a pretty good digital that I am using now. It's a pain in the neck to wait for
the display to stabilize when I measure anything with it, but I think that it is pretty accurate after a few seconds.

Tom in TN

Eman85 · Oct 26, 2015

Disconnect the sending unit from the gauge, with power to the gauge it should go past the full mark. Now ground the sending unit part of the gauge and it should go empty. That's the easy ck for the gauge itself. Only other way is using resistors or a variable resistor if you know the ohms range of the sender.

Resistance of sending unit for fuel guage

Tom in TN

Well-known Member

Dean

Well-known Member

Tom in TN

Well-known Member

Hobo,NC

Well-known Member

Tom in TN

Well-known Member

Eman85

Member

Similar threads