Fuel Sending Unit OHM Grounding Out

[testerdahl]

Hey Guys,

I've been working on getting a fuel gauge to work and I've spent hours reading threads on this forum. I just can't quite get it to work. My Father-in-law stopped by tonight and we both looked at it and tested the various items with a multi-meter.

I have a 1962 Chevy C10. I bought a new fuel sending unit from Eckler's (0-30 OHMs) and I bought a 0-30 OHMs fuel gauge from Equus. Links below.

We tested the grounds and found them all to be working correctly. Then, we hooked up the fuel gauge and it reads past full. Finally, we removed the fuel sending unit and tested continuity from the sender post to the body of the unit. We have continuity now and we wondering if we should have continuity between the sending unit post and the body.

I have another fuel sending unit I bought new that doesn't fit my truck. We tested that one and we have continuity as well.

Links:
https://www.ecklerstrucks.com/chevy-...1960-1966.html
https://www.iequus.com/7363.html

Here are some pics.

[ray_mcavoy]

Yes, you should be seeing a reading somewhere in the 0 to 30 Ohm range when you measure between the sending unit body & terminal post. The exact reading you get will depend on the position of the float arm. 0Ω should correspond to the float being in the empty tank position, and 30Ω should correspond to the float being swung up into the full tank position.

The gauge reading past full is usually an indication of an open somewhere in the sending unit circuit. You've already checked the ground and the unit itself so that pretty much leaves the wire that connects the sending unit to the gauge. A quick check for that is to temporarily ground the sending unit wire (that should make the gauge read empty). If not, use your meter to check that wire for continuity.

I believe the original wire routing for your 62 has the sending unit wire running over toward the driver side of the cab, up under the driver side sill plate, and then plugging into a receptacle on the fuse box. From there, it continues up through the dash harness to the instrument cluster plug. And finally from the cluster plug to the gauge.

[testerdahl]

Originally Posted by ray_mcavoy

Yes, you should be seeing a reading somewhere in the 0 to 30 Ohm range when you measure between the sending unit body & terminal post. The exact reading you get will depend on the position of the float arm. 0Ω should correspond to the float being in the empty tank position, and 30Ω should correspond to the float being swung up into the full tank position.

The gauge reading past full is usually an indication of an open somewhere in the sending unit circuit. You've already checked the ground and the unit itself so that pretty much leaves the wire that connects the sending unit to the gauge. A quick check for that is to temporarily ground the sending unit wire (that should make the gauge read empty). If not, use your meter to check that wire for continuity.

I believe the original wire routing for your 62 has the sending unit wire running over toward the driver side of the cab, up under the driver side sill plate, and then plugging into a receptacle on the fuse box. From there, it continues up through the dash harness to the instrument cluster plug. And finally from the cluster plug to the gauge.

Thanks. I'm talking about a different reading than the 0-30 OHM from the float.

[ray_mcavoy]

You're welcome. I don't quite understand what different reading you're talking about though.

In the first pic, it appears as though you have the black meter probe touching the metal case of the sending unit and the red probe touching the connection on the sending unit's variable resistor assembly. Measuring at that point should give you the same 0 to 30Ω reading as you'd expect to see with the red meter probe touching the terminal stud on the top of the sending unit assembly.

Edit: After re-reading your original post, I'm wondering of you're asking about continuity between the sending unit's variable resistor assembly and the terminal stud on top ... if so, yes, you should have continuity between those two points. If that connection were open circuit, you wouldn't see the 0 - 30Ω reading when measuring to the terminal stud and it would explain the gauge reading over-full.

[Foot Stomper]

Originally Posted by testerdahl

Thanks. I'm talking about a different reading than the 0-30 OHM from the float.

Surely you can give us more to work with than this vague reply.

[RustyPile]

I'm with Ray on this one.. I'm a bit confused as to your testing technique so let's back up and do some pre installation checks.. With the gauge hooked to the circuit and the sending unit removed from the tank, connect a jumper wire between the sending unit body (not the terminal post) and a good ground.. Connect the sending unit wire to the terminal post on the sending unit.. Turn on the ignition and swing the float slowly from empty position up to the full position, pausing at 1/4, 1/2, and full.. Allow a bit of time for the gauge needle to "catch up".. If the wiring, gauge, and sending unit all function properly, you should see the gauge needle indicate the various fuel level readings.. No volt/ohm meters or other test equipment is needed for this test.. If the test is passed, and your tank is properly grounded, install the sending unit and you're good to go. If the test failed, re-address your installation.. Test for grounds, shorts, and failed components..

When I suspect a bad sending unit, I use a "test resistor" composed three 10 ohm 3 watt resistors connected (soldered) in series.. Using jumpers, I connect one end of the test resistors to ground and the other end to the sending unit wire.. With the ignition turn on, the gauge should read "FULL".. Move the ground jumper from the end to between the 2nd and 3rd resistor.. The gauge should now read around 2/3 - 3/4 tank.. Move the jumper to the next resistor "gap" and the gauge should read still lower.. The exact reading isn't important, just that the gauge responds.. This test checks the gauge, circuit board, wiring, and voltage supply..

[raceman6135]

Originally Posted by testerdahl

Links:
https://www.ecklerstrucks.com/chevy-...1960-1966.html
https://www.iequus.com/7363.html

The Equus gauge you linked to is for a 240-33 ohm system, not the 0-30 ohm system (and float/sending unit) that you have in your truck.

That is likely the cause of some of the issues you're having.

I don't think Equus has a gauge that works 0-30 ohm. A few other manufacturers do, however; here is sample from Summit Racing (there may be others that they don't sell):

https://www.summitracing.com/int/sea...rder=Ascending

Hope that helps.

[bloo]

Testing from the connector on the sending unit to the flange that mounts in the tank should read 0 Ohms to 30 Ohms as you move the float arm around.

To work the gauge needs 3 connections. 1) +12v 2) Ground/-12v 3) A wire to the sender

To work the sender needs 2 connections 1) The wire from the sender and 2) Ground/-12v, the SAME ground the gauge has.

If you really have a 240-33 ohm gauge then raceman6135 nailed it. That cant work ever. You either need a 0-30 ohm gauge, or you need to adapt a 240-33 ohm sending unit to the tank.