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It worked fine before I tore my dash cluster apart again to fix my tach. When I turn on the key, the fuel gauge goes to 9:00. There is a half of a tank of fuel in it. When I disconnect the connector to the gauge and give the gauge 12 volts and ground from an outside source, it moves to half. If I disconnect the voltage and hook the connector back up and turn the key on, it goes back to 9:00. I have 12 volts with key on to pink wire. I have continuity from gauge ground terminal to the gauge housing and the black wire on temp gauge. Resistor reads correct 40 ohms for around half a tank. What could be going on? Thanks for the help!
Bob, I checked the ground stud on the back of the gauge and it is fine. Anyone have any other thoughts. This is driving me nuts and I just can’t think of anything else but that the gauge is somehow toast.
Thanks Tony, I have looked at every thread on here related to the fuel gauge, and have looked at all the great Willcox stuff. Interesting since I have never seen one instance where someone’s gauge is acting like mine. Never seen one go to 9 o’clock. If I power the gauge with an external 12 volts, it goes to where it is supposed to, even without the sender wire hooked up. Going to look at it again tomorrow. I did run a long wire and I do have continuity from the sender right to the gauge. This gauge was rebuilt, the resistor checks out and this thing worked fine 2 weeks ago. I did get pretty deep into the wiring to get my tach out, but I am at a loss of what I could have done. It is all new wiring as well. Thanks for the help!
Bill
Last edited by 69ttop502; Feb 5, 2021 at 07:48 PM.
To recap. I have 12 volts to the pink wire when using the ground stud on the gauge, so that tells me I have power and the ground is good. If I disconnect the plug from the gauge and power it externally, with or without the sender wire, the gauge moves to where it should, which right now is about half a tank. When I depower, the gauge stays there and at that point the sender measures 40 ohms, which is correct. As soon as I plug the connector back on the gauge and turn the key on, gauge goes back to 9 o clock.
I am going to pour 5 more gallons in the tank as maybe I am confusing 1/2 tank with the spot, around 1/4 tank where sender ground failure puts the gauge. Doesn’t make sense gauge goes there whether sender is hooked up or not.
Last edited by 69ttop502; Feb 5, 2021 at 07:56 PM.
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Originally Posted by 69ttop502
...When I disconnect the connector to the gauge and give the gauge 12 volts and ground from an outside source, it moves to half.
This condition should have cause the gauge to go to 3:00 position. There are only three things hooked up to the gage and here you have the 12 v and the ground now only. Seems like the problem is in the gauge itself as it is off about 90° to the left from the correct settings. There are two coils on the gauge...is it possible one of them got damaged?
Fuel Gauge Schematic
Last edited by Redvette2; Feb 5, 2021 at 09:14 PM.
Reason: Added Schematic
This condition should have cause the gauge to go to 3:00 position. There are only three things hooked up to the gage and here you have the 12 v and the ground now only. Seems like the problem is in the gauge itself as it is off about 90° to the left from the correct settings. There are two coils on the gauge...is it possible one of them got damaged?
Fuel Gauge Schematic
I guess it is possible although I never removed the gauge from the cluster, however I did remover the cluster from the bezel if i am calling the parts correctly. Thanks for this as it is the only attempt at an explanation for the 9 o’clock position of the gauge, and makes sense with my limited knowledge here. Thanks again!
Bill
Last edited by 69ttop502; Feb 5, 2021 at 09:24 PM.
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
You might want to check the gauge resistor value is 90 Ohms also...you will have to remove it to check due to the parallel coil. Doesn't seem likely with your reported issue but it is simple to verify.
I actually did test the resistor and it tested at exactly 90 ohms. I have no heater in my car so even though the center gauges are mounted, with the right side dash pad removed I can reach back there and was able to remove it to test. Thanks again.😀
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
A few other WAG ideas. Bad connection at the very back of the gauge. Measure what the actual 12 volts measurement is as close to the internal gauge's +12v and ground connections as possible. Also could the needle have been bumped loose off the shaft and now is just in the wrong position? I believe it should spin freely if no power is applied but shaft will tighten up when power is applied.
Last edited by Redvette2; Feb 7, 2021 at 11:07 AM.
I do not have a 69 Covette so I do not know if it is possible to read the voltage on the sender wire with the ignition on. If it is possible, here is what I would recommend: At a half tank, the voltage by my calculation should be about 4V. The calculation for this circuit is 45 Ohms(for half tank)/(90Ohms+45Ohms)*12=4VDC. So using the same method, a 3/4 full tank would read about 5.14VDC on the sender wire (67.5Ohms/(90Ohms+67.5Ohms)*12. Full will be 6V on the sender wire. You can replace the 12V in the calculation for what you are actually getting reading on your 12V supply at the guage. This will make you sender wire voltage calculation more accurate. If the sender wire is the proper voltage per the calculation above and you have 12V across the gauge, then I would suspect the gauge itself.
I hope you can find the issue. It can be very frustrating chasing these things.
Kind regards,
Mark
Strange fuel gauge behavior. Help!
