Another fuel gauge issue....

[Kimper]

I now this is a repetitive issue but can some one tell me how many wires are supposed run to the tank if my 76 Chevy K10 single tank. I have a red (or pink) on that runs to a little nipple type stud (and reads .500 ohms) on the fuel sending unit itself and a black wire that runs to a grounding tab then to the frame (and reads 2.0 ohms).My other question is my gauge reads full at this point. Can anyone point me in the correct direction of what I check next??  (The blue wire is just s jumper right to ground on the batter)

[hatzie]

The tan or pink wire goes to the gauge through the big square bulkhead plug.
You measured .5 ohms from the sender stud to the retaining ring? 
Is the tank empty?
Empty should read roughly 0 ohms and full roughly 90 ohms from the sender stud to the tank and the top of the sender.  A half ohm is close enough to zero to put the gauge needle at E with the key on.

That blue wire should run from a 1/4" blade disconnect on the sender retaining ring or welded in sender bung to a ring terminal on the frame. It's supposed to ground the tank and complete the sender circuit.  The stock ground wire color is black.  If it's missing... the gauge needle will sit at approximately 3:00 with the key on.  Grounding on the battery will work for testing tho.





From orbit on my Android.

[Kimper]

I have about 10-15 gallons in the tank as it sits, is there something else I could check at the gauge or does it seem like a sending unit??

[hatzie]

Assuming costs money.  Troubleshooting is free.
If the sender is exposed enough to take your picture then it can be tested right at the sender.

If you want to be hard way Harvey... remove the fuel gauge from the housing it'll expose the gauge connection clips inside the housing. 
Assuming the following starred list conditions are met you can test the sender ohmage from the gauge ground clip to the gauge sender clip inside the housing.
Again ALL of the following MUST be TRUE to have a valid test at the gauge housing connections.
*The sender wire has no breaks between the tank & cluster.
*The sender wire is making good contact at the sender stud.
*The tank is properly grounded from the sender to the frame.


From orbit on my Android.

[Irish_Alley]

when you tested the ohms of the pink wire did you test it right to a clean ground strap that showed good as a ground?

[hatzie]

The only valid test on the sender wire would be ohming it from end to end with the ends unplugged.  Measuring from a ground to the sender wire is meaningless.

Remove the gauge and unplug the sender.  Hook the probes to the sender wire on both ends.  Ohmage should be zero or darn close.


From orbit on my Android.

[Irish_Alley]

Measuring from a ground to the sender wire is meaningless.

by doing this wouldnt that test just the sending unit vs testing the sending unit + wires to the cluster

[hatzie]

Measuring from a ground to the sender wire is meaningless.

by doing this wouldnt that test just the sending unit vs testing the sending unit + wires to the cluster

From orbit on my Android.

His picture in the OP is of the sender.  I am assuming he is talking about testing on that end.

If he unplugs the sender and tests from the pink wire to a ground he is ohming the gauge coils not the sender.  The sender isn't in the circuit....  it's unplugged.  That's not a useful measurement.

To ohm the sender as shown in the picture...
Unplug the pink wire.
Ohm from the stud where the pink wire was connected to the top of the sender or the tank. 
 You can then ohm from that stud where the pink wire was connected to the frame.  If the readings don't match likely the frame to tank ground wire is bad.
With 15 gallons in the tank the meter should read between 50 and 80 ohms at the sender.  If it reads 0 ohms or something lower than 50 there is a problem.
I used to have a spreadsheet where I plotted the sender ohmage needed to drive the gauge needle to certain positions.

[Irish_Alley]

i think i understand you. youre saying to test it post to post on the sending unit with the wires unplugged. then test the wires

but i wasnt trying to say test the pink wire but i did say that lol. i meant testing the pink wires connection to a ground

[Kimper]

I removed the sending unit and ohmed it from the stud to the sending unit itself and got 14.5 ohms on empty and 109.7 on full which tells me the sending unit is bad.. Am I correct people??

[bd]

Did you short the ohmmeter leads together and "zero" the meter before taking the measurements?

[hatzie]

I removed the sending unit and ohmed it from the stud to the sending unit itself and got 14.5 ohms on empty and 109.7 on full which tells me the sending unit is bad.. Am I correct people??

Not good but it should still drive the gauge.
On a perfect unit 90Ω=F  &  0Ω=E  In practice 86Ω - 94Ω will read close enough to full and 5Ω will read close enough to E
Your sending unit will drive the gauge a little high but it should work.

I found my spreadsheet.

Ωs   Gauge Reads
90   F
76   7/8
64   3/4
53   5/8
45   1/2
37   3/8
29   1/4
18   1/8
00   E

[Kimper]

i hooked up the sending unit to the gauge when thebunit was out if the truck and gauge did follow so either A, I just deal with the fuel gauge being off or B, I get a new sending unit...

[Kimper]

Another quick question, my tank is on the passenger side and the float on the sending unit faces forward. Does this matter if it faces forwards front of the truck or the rear??

[hatzie]

There are RH & LH senders in the parts books so something is different.   
It may work just fine to rotate a sender or it might not clock to the proper position for the pipes exiting.  I'm not sure... 
You usually need 3 pipes.  Vapor, Return, & Feed.  There are senders for trucks without the return line.