fuel gauge test
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Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
fuel gauge test
How can I go about testing my fuel gauge with it in the cluster?
The gauge reads full with the key on. It has been like this for a long time. I assumed it was a bad sending unit. I guess I was wrong since a new sending unit is doing the same thing.
I should have tested the sending unit before installing it but it was hot and I was not clearly thinking.
I jumpered a wire off the negative battery post to the sending unit post (My thinking was maybe I just had a bad ground off the frame) gauge still pegged past full.
So now I'm guessing it is a bad/grounded power wire. (or a bad sending unit, but anyway..)
Anyway can I jumper a wire from one of the posts of the fuel gauge to the sending unit for testing purposes?
If so does it matter which post I jumper to? Will this even work?
I assume this would be easier than tearing into the loom under the vehicle/disturbing old wiring and possibly causing more problems.
The gauge reads full with the key on. It has been like this for a long time. I assumed it was a bad sending unit. I guess I was wrong since a new sending unit is doing the same thing.
I should have tested the sending unit before installing it but it was hot and I was not clearly thinking.
I jumpered a wire off the negative battery post to the sending unit post (My thinking was maybe I just had a bad ground off the frame) gauge still pegged past full.
So now I'm guessing it is a bad/grounded power wire. (or a bad sending unit, but anyway..)
Anyway can I jumper a wire from one of the posts of the fuel gauge to the sending unit for testing purposes?
If so does it matter which post I jumper to? Will this even work?
I assume this would be easier than tearing into the loom under the vehicle/disturbing old wiring and possibly causing more problems.
FTE Legend
Joined: Nov 2015
Posts: 30,906
Likes: 4,122
From: Angier, NC
I take it the oil & temp gauges if you have them are working good? I ask because the IVR is for the gas, temp & fuel gauges.
To see if it is the sender remove the wires from the sender and turn the key on does the gauge still peg full? If so then I would think the wiring is the issue.
Is there a plug between the trucks harness and the wiring harness to the rear lights / sender? If so unplug and see if it still pegs full.
If it does not peg you know the rear / sender harness is the issue.
I don't know the back of the cluster but the IVR sends about 5 volts to the gas, temp & oil gauges and then out to the senders. If you were to check the wires with a test light it will blink.
You will need to check the cluster to see what side of the gauges get the power from the IVR so you can remove the other wire for testing.
Sorry I cant be of more help.
Dave ----
To see if it is the sender remove the wires from the sender and turn the key on does the gauge still peg full? If so then I would think the wiring is the issue.
Is there a plug between the trucks harness and the wiring harness to the rear lights / sender? If so unplug and see if it still pegs full.
If it does not peg you know the rear / sender harness is the issue.
I don't know the back of the cluster but the IVR sends about 5 volts to the gas, temp & oil gauges and then out to the senders. If you were to check the wires with a test light it will blink.
You will need to check the cluster to see what side of the gauges get the power from the IVR so you can remove the other wire for testing.
Sorry I cant be of more help.
Dave ----
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Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
Yes the IVR works. I get the pulse and it shows with a test light as well.
For anyone searching in the future..
Looking at the dash, the "power post" of the fuel gauge is on your right. You can determine this by connecting a test light to it and you will see it pulse.
I jumpered this post to the sending unit "power" post and my gauge read correctly.
So that confirmed to me that there is a short in the wire running from the cluster to the sending unit.
Also if you take a piece of wire and touch both posts to the gauge, it should drop to E as well.
I'm going to run a new wire from the gauge to my sending unit. I sure don't feel like tampering with that harness.
For anyone searching in the future..
Looking at the dash, the "power post" of the fuel gauge is on your right. You can determine this by connecting a test light to it and you will see it pulse.
I jumpered this post to the sending unit "power" post and my gauge read correctly.
So that confirmed to me that there is a short in the wire running from the cluster to the sending unit.
Also if you take a piece of wire and touch both posts to the gauge, it should drop to E as well.
I'm going to run a new wire from the gauge to my sending unit. I sure don't feel like tampering with that harness.
Thread Starter
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Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
SO... yea that isn't working now.. I gave up for the night. I'm pretty sure nothing is touching on the sending unit. The jumped wire from gauge to sending unit on positive side is not working and I added the battery ground jumped wire back in with same results.
Makes no sense to me, it worked on my trial or so it appeared..
Gauge still goes to E when shorting both posts on the gauge itself. If it isn't raining tomorrow I'll try and figure it out..
Anyone feel free to chime in if I am mistaken on "hot wiring" this.. Going to double check the IVR is still working, when I tested my new "hot" wire to the sending unit with my multimeter it was showing 11 to 0 but was pulsing so I figured my multimeter was acting up. I'll have to check tomorrow again..
Makes no sense to me, it worked on my trial or so it appeared..
Gauge still goes to E when shorting both posts on the gauge itself. If it isn't raining tomorrow I'll try and figure it out..
Anyone feel free to chime in if I am mistaken on "hot wiring" this.. Going to double check the IVR is still working, when I tested my new "hot" wire to the sending unit with my multimeter it was showing 11 to 0 but was pulsing so I figured my multimeter was acting up. I'll have to check tomorrow again..
Elder User
Joined: Apr 2018
Posts: 567
Likes: 3
You should have tested the sending unit before installing it, not telling you anything you don't already know but there's always the possibility it's bad, even though new.
No need to go down a rabbit hole chasing other potentially false problems if the sending unit is at fault, I would at least try to rule that out first.
No need to go down a rabbit hole chasing other potentially false problems if the sending unit is at fault, I would at least try to rule that out first.
More Turbo
Joined: Sep 2003
Posts: 514
Likes: 27
I recently bought two senders, one for 19 gallon behind axle tank and one for 33 gallon Bronco tank. The stock Ford unit for the 19 gallon tank was farther off the 10 - 90 ohms standard than the aftermarket one from Jeffs Bronco Graveyard. Both, though, are close enough for me.
R.
R.
Fleet Mechanic
Joined: Dec 2007
Posts: 1,505
Likes: 339
From: Wildwood Pa
Remove any jumper wires you have installed, go back to just factory wiring.
Unplug the sender at the tank. Turn the key on. If the fuel gauge still pegs, you have a short to ground in the wire that runs from the sender to the gauge cluster. Trace every inch of the wire, looking for worn insulation, where it can touch metal or another worn wire, & repair.
If the gauge does not peg when the sender is disconnected, your sender has a short to ground. Remove the sender, test it & repair.
I recommend NOT shorting both posts on the fuel gauge. That is a good way to burn up the gauge, IVR, PC, or burn the whole truck down.
If your temp & oil gauge work correctly, your IVR is still good.
Unplug the sender at the tank. Turn the key on. If the fuel gauge still pegs, you have a short to ground in the wire that runs from the sender to the gauge cluster. Trace every inch of the wire, looking for worn insulation, where it can touch metal or another worn wire, & repair.
If the gauge does not peg when the sender is disconnected, your sender has a short to ground. Remove the sender, test it & repair.
I recommend NOT shorting both posts on the fuel gauge. That is a good way to burn up the gauge, IVR, PC, or burn the whole truck down.
If your temp & oil gauge work correctly, your IVR is still good.
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Thread Starter
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Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
Remove any jumper wires you have installed, go back to just factory wiring.
Unplug the sender at the tank. Turn the key on. If the fuel gauge still pegs, you have a short to ground in the wire that runs from the sender to the gauge cluster. Trace every inch of the wire, looking for worn insulation, where it can touch metal or another worn wire, & repair.
If the gauge does not peg when the sender is disconnected, your sender has a short to ground. Remove the sender, test it & repair.
I recommend NOT shorting both posts on the fuel gauge. That is a good way to burn up the gauge, IVR, PC, or burn the whole truck down.
If your temp & oil gauge work correctly, your IVR is still good.
Unplug the sender at the tank. Turn the key on. If the fuel gauge still pegs, you have a short to ground in the wire that runs from the sender to the gauge cluster. Trace every inch of the wire, looking for worn insulation, where it can touch metal or another worn wire, & repair.
If the gauge does not peg when the sender is disconnected, your sender has a short to ground. Remove the sender, test it & repair.
I recommend NOT shorting both posts on the fuel gauge. That is a good way to burn up the gauge, IVR, PC, or burn the whole truck down.
If your temp & oil gauge work correctly, your IVR is still good.
Traced the wiring, it looks good up to the cab, Lose it when it gets to the cab, not really crazy about cutting/peeling into electrical tape and potentially nicking other wires in the process..
Multimeter on the posts shows the IVR working as intended. Jumped Wire from gauge to the sending unit even shows voltage fluctuation..
Still no gauge response when attempting to jump/bypass, if it's even possible to bypass this.
Thought maybe I could tie into the orange wire (diagram shows this as fuel gauge wire) going to the cluster but that doesn't seem to do anything. foil looks to have had better days as well.
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Fleet Mechanic
Joined: Dec 2007
Posts: 1,505
Likes: 339
From: Wildwood Pa
It can be hard to find a bad spot in the wire while under the truck. You can cut the wire running from the sending unit to the cab in a spot close to the cab, & repeat the test, see if the gauge still pegs. If it doesn't peg you know the short is in the section of wire between the cut & the sender. Run a new wire to replace that section to fix.
If it still pegs after cutting the wire the short in the wire would have to be in a spot you can't access, like in the cab.
You could cut the orange wire close (3-4") to the harness plug, the one that goes to #15. Test it, key on & see if the the gauge still pegs. If it does peg, that narrows it down to something shorted in the cluster. No peg, run a new wire from the cluster plug orange wire # 15 to the sender & test.
Test the fuel gauge too. Use a 1.5 V battery & two wires with clips on the ends. Clip a wire to each terminal on the fuel gauge, other end to the 1.5V battery. You may have to reverse polarity on the battery to make the gauge work. Gauge should slowly rise to about 1/4. Add another battery & it should go to about 3/4. This test will at least let you know the fuel gauge is working like it should. You can test it with the gauge in the cluster.
If it still pegs after cutting the wire the short in the wire would have to be in a spot you can't access, like in the cab.
You could cut the orange wire close (3-4") to the harness plug, the one that goes to #15. Test it, key on & see if the the gauge still pegs. If it does peg, that narrows it down to something shorted in the cluster. No peg, run a new wire from the cluster plug orange wire # 15 to the sender & test.
Test the fuel gauge too. Use a 1.5 V battery & two wires with clips on the ends. Clip a wire to each terminal on the fuel gauge, other end to the 1.5V battery. You may have to reverse polarity on the battery to make the gauge work. Gauge should slowly rise to about 1/4. Add another battery & it should go to about 3/4. This test will at least let you know the fuel gauge is working like it should. You can test it with the gauge in the cluster.
Thread Starter
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Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
Battery test worked.
I poked a wire into #15 with the orange connected still to try and make a connection. It makes sense if orange is grounded out it probably was the reason I didn't see anything on the multimeter or a reaction on the gauge. I was able to pull the orange connector pin out. Know anyone that sells those pins? I wouldn't mind waiting and crimping one onto a new wire instead of cutting and butt connecting. Not much slack anyway on that wire. Probably easier to just find a used harness plug with the wires cut..
This truck could use a new harness but I'm not sure its worth the cost/labor yet.
I poked a wire into #15 with the orange connected still to try and make a connection. It makes sense if orange is grounded out it probably was the reason I didn't see anything on the multimeter or a reaction on the gauge. I was able to pull the orange connector pin out. Know anyone that sells those pins? I wouldn't mind waiting and crimping one onto a new wire instead of cutting and butt connecting. Not much slack anyway on that wire. Probably easier to just find a used harness plug with the wires cut..
This truck could use a new harness but I'm not sure its worth the cost/labor yet.
Thread Starter
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Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
Do you happen to have any cluster connectors laying about? I didn't see any on the marketplace or ebay unless I buy the cluster itself.