Frustration ! In cab fuel sending unit inop.

[54blackhornet]

I recently bought the correct send unit for my 71 C/20. Following the instructions I inserted it along with new gasket and sealing ring. Tank is grounded well to cab. Tan wire from sending unit is plugged into the fuel gauge input on fuse panel. With key on gauge is stuck at 3PM. Disconnect and grounding tan wire gauge still stuck at 3PM. I even tried grounding the sending unit directly to the negative battery post, nothing ! Would pulling the firewall connector where all the wires enter cab help ? Loose connection or corrosion ?

[1970cstblazer]

If it is continually at the 3 o'clock, the circuit has extremely high to infinite resistance. Check grounds and all connections. If you have a VOM, test the continuity. If you ground out the tan wire, the gauge should swiftly return to empty or just below empty.

[pjmoreland]

The fuel gauge wire does not pass through the firewall, so there's no need to check the firewall connector for this issue. Your sender is probably fine. The fuel sender wiring follows this path:

1) Tan wire runs from tank sender and plugs into the fuse panel "Fuel Ga" terminal

2) Another tan wire runs from the back of the fuse panel up to the connector that plugs into the back of the gauge cluster

3) A copper trace on the gauge cluster flexible circuit board runs to the passenger side post on the back of the fuel gauge

As 1970cstblazer said, there is a continuity issue (a break) along this route. You could either use a multimeter or a test light to check for continuity between the passenger side post of the fuel gauge and the end of the wire that connects to the sender.

Another approach would be to ground different points along this route to see if the gauge will move to EMPTY. You could start by grounding the "Fuel Ga" terminal at the fuse panel. If that doesn't work, then try grounding the passenger side terminal at the gauge. The ignition switch must be in the run position (engine doesn't need to be started though) for the grounding tests to work.

[michael bustamante]

also check that tan wire!..it runs along the driver side seat and could be chaffed up or even split and corroded.

[54blackhornet]

Guys I appreciate the input. I have pulled the tan wire out and checked it for continuity and any sign of cracking or bare spots, all checked out good. The sender is brand new from Wes in Olympia. Tank is properly grounded in multiple locations. Beginning to think the problem is with the gauge itself or within the cluster. I will continue the search…

[dmjlambert]

On your previous thread on the subject you were going to pull the instrument cluster and work on it. Did you get a round tuit?

[RustyPile]

I've read completely through BOTH your threads on this issue.. You've stated in both of them that you have thoroughly tested/checked the tan wire between the fuse box and sending unit.. But nowhere have you said anything about the tan wire that runs from the fuse box to the cluster plug. Have you checked this section of the tan wire?? There is no fuse in this wire. The fuse box is just simply used for a connection point for that part of the fuel gauge circuit..

It is an established fact that you have an open circuit. The next place you need to check is the tan wire leading to the instrument cluster plug.. Disconnect the instrument cluster plug and locate the tan wire in it. Using a DVM set to read continuity, connect one test dvm lead to the tan wire at the fuse box. Connect the other dvm test lead to the tan wire at the cluster plug.. If you have continuity, the problem is probably in the printed circuit or the gauge itself.. THEN you can remove the gauge cluster...

[54blackhornet]

Thanks again ! The reason I started another post is because I could not find the other one ? I tried searching for it ? Will be pulling cluster out next..Jack

[michael bustamante]

also, make sure you guages are grounded

[54blackhornet]

The cluster has never been removed, is it likely that it could loose ground?

[RustyPile]

Originally Posted by 54blackhornet

Thanks again ! The reason I started another post is because I could not find the other one ? I tried searching for it ? Will be pulling cluster out next..Jack

Your other thread is right here:

http://67-72chevytrucks.com/vboard/s...d.php?t=846008

Originally Posted by 54blackhornet

>>>>>>>snip<<<<<<<<..... Will be pulling cluster out next..Jack

Did you not read the second paragraph in post #7, paying close attention to the second sentence???????

With all due respect ,sir.. When troubleshooting electrical problems, you have to go about it systematically. Guessing, skipping over components, and chasing "hunches" is not a systematic method...

[54blackhornet]

Thanks Rusty ! You remind me of Sister Cabrini in 4Th grade science class !…I will follow your directions explicitly from now on…

[RustyPile]

Originally Posted by 54blackhornet

Thanks Rusty ! You remind me of Sister Cabrini in 4Th grade science class !…I will follow your directions explicitly from now on…

Sister Cabrini had a point to make.... So do I..

Sarcasm aside, It's very easy to track down a coolant leak or oil leak... Simply back track the "trail" they leave behind... Electrical "leaks" are more difficult to track down.. Invisible electrons travel through a wire and don't "leave a trail" so to speak, when they go astray.. First, you have to fully understand how electricity works in a circuit, of which there are several types. Follow a methodical troubleshooting technique and knowing how to use and operate test instruments that "read" those electrons is mandatory.

In your case, the gauge symptoms indicate an open (broken wire, disconnect at a plug, or loose connection at a plug) in the tan wire.. Start at either end and work toward the other end, testing it's continuity.. Don't check half the length and then arbitrarily assume the gauge is bad and start removing the cluster.. You could very well be adding unnecessary work.. And also, you could very easily add another problem to the mix.