Fuel sending unit wiring

Jun 7, 2018
37
5
18
52
Dublin, OH
#1
I have a 1991 lx v8, and am trying to wire a custom fuel gauge. It is with the Holley hp efi system, but it’s not getting a reading. I have the yellow/white wire from the dash connector wiring into it and it is setup as a custom ohms input, but does not display a read out, meaning ♾ ohms, because it reads as 100% full no matter the scaling or boundaries. I have tried looking at wiring diagrams for the sender but I can’t figure it out. I assume the sender is grounded on its own away from the dash cluster connector, but I could be wrong. If anyone could help, it would be much appreciated.
 
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a91what

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Mod Dude
Apr 6, 2011
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#2
does the input have a built in Vref?? if it does not have a pullup to 5v the ohmic value cannot be read it is still an ADC input.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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#3
Just to be clear, are you wiring an aftermarket (holley) sender to the factory gauge?
 
Jun 7, 2018
37
5
18
52
Dublin, OH
#8
Post link to the document please. You may have to build a circuit.
Maybe a better question is how would I wire a circuit through a multimeter to see if the sender is working properly? As in, wire a circuit and if I get a good ohms reading, I know it’s right.
 

a91what

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Apr 6, 2011
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#9
Maybe a better question is how would I wire a circuit through a multimeter to see if the sender is working properly? As in, wire a circuit and if I get a good ohms reading, I know it’s right.
Simple test from the sender to ground
 
Jun 7, 2018
37
5
18
52
Dublin, OH
#14
Ok do some testing before dropping the tank.
I didn’t an ohm test, positive test on the yellow/white fuel sender wire, negative on the negative battery terminal, and it read about 56 ohms. Would me completely removing the factory gauge cluster and only jumping the green/red wire to a switched +12v source mess with the grounding of the sending unit?
 

a91what

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Apr 6, 2011
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#15
yup that sounds to be correct, where do you have the ground for the holley dash coming from? you may want to consider re-grounding the dash and see if the signal comes up.
 
Jun 7, 2018
37
5
18
52
Dublin, OH
#16
yup that sounds to be correct, where do you have the ground for the holley dash coming from?
The CAN bus has a ground that goes directly to the battery. It goes battery, can bus, dash, then back to the battery
 

a91what

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Mod Dude
Apr 6, 2011
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#17
ok... the canbus is usually reserved for communication with the ECU. let me look at the wiring diagram again.
 
Jun 7, 2018
37
5
18
52
Dublin, OH
#18
ok... the canbus is usually reserved for communication with the ECU. let me look at the wiring diagram again.
Okay, not sure if you saw me edit my earlier post, the only cables I messed with from the factory dash connectors were the red/green that I attatched to a switched source, and the yellow/white fuel sending unit wire, I’m wondering if me not changing any ground messed it up
 

a91what

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#19
not sure without knowing how the holley is wired. trying to help on my phone is a pain. lol
 

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