Fuel Gauge tech questionGround the sending unit wiring to a good chassis ground (instead of the sending unit housing) an

[Lambo]

In the fuel tank tank area on this site, when testing for fuel gauge not working, its says this "Ground the sending unit wiring to a good chassis ground (instead of the sending unit housing) and watch the gauge." There are two wires, black and orange, so which wire is to be grounded to chassis ground?

[HIO Silver]

I'd go with the black as the ground... the other is prolly the signal wire to the gauge itself.

Ya could read the schematics provided by Fordification to verify....

[Lambo]

Thanks HIO Silver, I will give that a try.

[Busboy]

You would ground the orange wire which is the one that normally goes to the sending unit. This tells the gauge that the tank is full. If the gauge pegs out to full then the problem is in your sending unit or the ground wire to the sending unit, the black one that screws to the sheet metal.

[Lambo]

OK, thank you for the clarification. I tried that but the gauge did not move. I presume I should be grounding the orange wire while it is disconnected from the sending unit terminal, correct? If so, I may need to try a good chassis ground and try again. I didn't think the ISVP unit on the back of the dash would be bad if the other gauges work, which they do, but maybe that is an incorrect assumption? Thanks for your help.

[Busboy]

Yes, you should ground the orange wire while it is disconnected from the sender. If you have an auxiliary tank switch I would make sure it is in order and to the correct tank sender. You might want to pull the instrument cluster out which is ridiculously easy and check continuity from the orange wire at the gauge (which is the one that goes to the sending unit) to the orange wire at the tank sender. If there is no continuity then you've got some wire tracing to do. There is a separate harness if you have an auxiliary tank that may have become disconnected.

[Lambo]

I have the dash out already and never thought about checking the continuity on the wire but will do so. I do have an aux. tank lever, but it is not hooked up that I can see. My truck was converted to a flat bed dually setup a long time ago and has a custom made aux tank with the flat bed. Thanks again.

[Busboy]

Let us know what you find.

[Lambo]

Well, the gauge is working but don't really know what I did to fix it. The orange wire did have continuity and grounding the orange wire to frame ground did not do anything. I disconnected the wire plug to the aux. tank switch and switched it back and forth several times. Maybe that is what did it. Now on to why the brake light is staying on. Ya gotta love old trucks.