Fuel scending unit

1962 C 130 got the lights fixed and now my fuel gauge quit but I was having trouble with the sending unit sticking once before How do they work? I no that the float goes up and down to read the tank but do they get any voltage to them what sends it back to the fuel gauge from the float. and can you test them by reading ohms

The sending unit is basically a variable resistor inline between the fuel gauge power and ground. Some read full at top ohms and some at 0 ohms. I got a J@@p unit for the aux tank on my A series and fabbed an adapter for the sending unit hole in the Ponti@c van tank that I'm using since it has same ohm arrangement and rating. If it sticks it could be the unit, or the gauge itself.

Here's a basic diagram:

Thats what I needed thank you. Some place I read the old units used between 30 an 300 ohms I,ll check that today then I read that two double A,s 3 volts can be used to test the gauge is that sounding right? Also have not had the sending unit out of tank yet It looks like you turn it to come out after screws are out does it matter right or left I don,t want to mess up the gasket

might go ahead and pick up some gasket material just in case. That gasket has been on there for a long time. I think, but could be wrong, that all you need is to take the screws out and pull the unit up. If I remember correctly, these old units do not need to twist. It could just be a separate ring that moves. Been a long time since I took one out. Do make sure you figure orientation of the float arm so when you put it back that it is in the same position.
Just my thoughts

Ok I took out the front seat to get a good look at the top of the sending unit. It did not look bad. Then I took the wire off I only have one going to it. I grounded it out and the gauge moved thats good new the gauge is good. I cleaned this wire off a few years back so I cleaned it off again with some sand paper cleaned the top and bottom nuts also put them back and it looks like it is working but I don,t trust it does any vender sell sending units to fit the old tanks and if so who? Has any one done one? thanks

I don't know trucks that old, but I do have several newer ones, from '66 through '73. Each has a ring that slides around to release the fuel sensor. Also, the service manuals I have for both series tell me that the fuel sensor is 0 to 90 ohms, empty to full. This is the same resistance that Chevy are supposed to have. My understanding of electricity tells me that 90 ohms is 90 ohms, regardless of who made it. However, where is the ground circuit? All the sensors I have ever seen have one somehow.Ford, Chevy, Dodge and IH have one. I haven't put a Chevy gas tank in a IHC truck of mine as of yet, but I have wondered about it. Especially if I got the proper mounting brackets at the same time. Then all that would be needed would be to see if it fits, has the right fit hose size, and gas hose size. This would definitely be something to think over before doing. However, where is the ground Hopefully, it will give you ideas on how to proceed. Others will weigh in on this, I hope. This forum is great for that. Hope it all goes well, Bill

I could be off, but ground on a one wire system is generally through the way it is bolted to the frame. Good grounds throughout are really important. If the unit is held in by a ring that makes contact with the unit and the rest of the tank, That is your "ground" path, then on through the bolt connections holding the tank to the cab or chassis as the case may be. If the unit functions and the arm on the float inside the tank is good, "grounds" was your issue and I would not look at replacing what is not really broke. Just my observation and thoughts.
Lloyd

A little dielectric grease on the electrical connections will go a long way to keep corrosion down and ensure a good contact.

I could be off, but ground on a one wire system is generally through the way it is bolted to the frame. Good grounds throughout are really important. If the unit is held in by a ring that makes contact with the unit and the rest of the tank, That is your "ground" path, then on through the bolt connections holding the tank to the cab or chassis as the case may be. If the unit functions and the arm on the float inside the tank is good, "grounds" was your issue and I would not look at replacing what is not really broke. Just my observation and thoughts.
Lloyd

So is this the case for a '68 Tall? I've been having issues with inaccurate readings on my gauge and decided to drop the tank and look at the sending unit. I was a little confused when I saw one wire connected the sending unit and another just dangling there. The truck was "restored" 12 years ago or so by someone else and the gauge is not original and now I'm assuming the previous owner ran a second useless wire for some reason. I still need to test the ohms on the sending unit and test the gauge but this would clarify the proper wiring.

Does anyone have a source for a C series sending unit? I've searched around and the ones I have found say they are for my truck '67 1200b) but all have much shorter arms for the float. Thank you