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fuel guage

Okay, I have my truck running really good now , just tuned it up. I do however have a small problem, the gas guage. It always reads full, I checked the sending unit by taking off the wire and grounding it and it then goes to empty. There is only one wire on it so I assume the tank is grounded to the chassis. I put a test ground wire to the sending unit but it did not change a thing. It reads 66 ohms which is about right for a 3/4 tank full of gas which I believe it has. when I take the wire off the sending unit the guage goes past full if I don't ground it. So how do I test the guage and what am I doing wrong ? Thanks


Texas Chapter member
If you take the sending unit out and ground it, does the gauge react when you manipulate the arm up and down?

If it has never worked since you got the truck, it would be worth finding out exactly what kind of gauge it is and make sure the sending unit and gauge are compatible.

On the gen 6 trucks there is a little voltage regulator that can go bad making the gauges act up. Might be worth looking in to.
the guages are VDO . It's crazy because now the speedometer doesn't work. It's all electronic no cable. As far as the gas guage, I was trying to avoid taking out the sending unit until I know for sure if it is the guage or not. I guess that will be the way to find out though.


Texas Chapter member
I think it would be worth double checking all the grounds. Make sure you have good engine to frame, engine to body, and body to frame(cab and bed) grounds. Unless the system has a dedicated negative connection, grounds can make a huge difference.
I'm still working on the speedo but I changed the sending unit and that solved that problem. In the meantime I'm going to use a gps to tell me my speed.

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