Gas Gauge/sending unit issues…

[inkslingrrr]

OK, so back to you gurus for some assistance.
I replaced the gas tank in my ‘71 c10 from the behind the seat version to the bed rails kind from LMC. Now with a full tank, the (stock) gauge reads just under half. Tested the sending unit seems to work OK, pulled it out tested it by hand, Can still only get it to read just under half. Where do I start. Should I believe this is the resistors on the old gauge?
Once I learn to post pictures I’ll get some on here

[Palf70Step]

Check for a good ground to the sending unit. That will mess with the gauge.

[inkslingrrr]

Originally Posted by Palf70Step

Check for a good ground to the sending unit. That will mess with the gauge.

Sending unit ground is good

[pjmoreland]

Is the new sender a 0-90 Ohm type? The sender resistance should be around 0 Ohms at empty and 90 Ohms at full.

Did the gauge work correctly with your original sender?

[inkslingrrr]

Originally Posted by pjmoreland

Is the new sender a 0-90 Ohm type? The sender resistance should be around 0 Ohms at empty and 90 Ohms at full.

Did the gauge work correctly with your original sender?

Yes it sure did

[RustyPile]

Originally Posted by inkslingrrr

OK, so back to you gurus for some assistance.
I replaced the gas tank in my ‘71 c10 from the behind the seat version to the bed rails kind from LMC. Now with a full tank, the (stock) gauge reads just under half. Tested the sending unit seems to work OK, pulled it out tested it by hand, Can still only get it to read just under half. Where do I start. Should I believe this is the resistors on the old gauge?
Once I learn to post pictures I’ll get some on here

If the circuit is wired correctly and the grounds are good, it sounds like you have the wrong sending unit. With a full tank, a 30 ohm sending unit will read just under 1/2 tank when connected to a 90 ohm gauge.

[pjmoreland]

Originally Posted by inkslingrrr

Yes it sure did

That sure points at the new sender as the problem then.

If you have a multimeter, it would be good to measure the resistance of the sender to see if it has a 0-90 Ohm range.

[inkslingrrr]

Originally Posted by RustyPile

If the circuit is wired correctly and the grounds are good, it sounds like you have the wrong sending unit. With a full tank, a 30 ohm sending unit will read just under 1/2 tank when connected to a 90 ohm gauge.

So nowhere in LMC catalog do I see a order # for a 90 ohm sender****

[pjmoreland]

A stock fuel gauge is designed to work with a 90-ohm sender. See post #3 of the following thread for an explanation of how to test the resistance of your LMC sending unit.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

[inkslingrrr]

Originally Posted by pjmoreland

A stock fuel gauge is designed to work with a 90-ohm sender. See post #3 of the following thread for an explanation of how to test the resistance of your LMC sending unit.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

So yeah, this is test it out as a 0 to 35 ohm sending unit… Now to find the right one or use a fuel bridge, need to thank everybody for their assistance because this is a little bit too techie for this old man!! thanks again

[RustyPile]

Originally Posted by inkslingrrr

So yeah, this is test it out as a 0 to 35 ohm sending unit… Now to find the right one or use a fuel bridge, need to thank everybody for their assistance because this is a little bit too techie for this old man!! thanks again

What's a fuel bridge?? [EDIT] Never mind, I found the answer...