Fuel Gauge reads full when truck is off! Help

[Cesar Diaz]

1972 C10 Cheyenne: Original gauge cluster

I replaced the gas tank and the fuel sending unit in this C10 we just got. When the truck is turned off, the tank reads full, When I turn the truck on, the Gas Gauge goes down to empty, not sure whats causing this. Before I installed the sending unit I tested it and everything was fine, down it would read empty and if i raised it, the needle would move up.

Any help would be appreciated.

I also have a second tank who's sending unit also works and when I switch to that tank it does the same, I am using an off-on-off switch. When I bypass the switch the same is happening.

[LockDoc]

Originally Posted by Cesar Diaz

1972 C10 Cheyenne: Original gauge cluster

I replaced the gas tank and the fuel sending unit in this C10 we just got. When the truck is turned off, the tank reads full, When I turn the truck on, the Gas Gauge goes down to empty, not sure whats causing this. Before I installed the sending unit I tested it and everything was fine, down it would read empty and if i raised it, the needle would move up.

Any help would be appreciated.

I also have a second tank who's sending unit also works and when I switch to that tank it does the same, I am using an off-on-off switch. When I bypass the switch the same is happening.

Are you sure the Brown fuel sender wire is connected to the correct spade terminal on the fuse block? It should be plugged into the "FUEL" terminal.

LockDoc

[71CHEVYSHORTBED402]

Safe to say your gauge worked with the old tank?

[CST10]

Mine did that for a while. It ended up being a grounding issue. After I ran an additional ground wire from the back of the bezel to some solid metal it went away.

[Cesar Diaz]

Thank you everyone, to answer everyone in one post:

Yes the brown wire is plugged into the right place on fuse panel

The old tank and sending unit was rusted to heck so no it did not work,

I tested the saddle tank sending unit before i installed and i tested the main tank sending unit before install and all was fine.

And I will look into grounding the terminal. Its almost as if the wiring is backwards.

[71CHEVYSHORTBED402]

If it helps..........This is per my gauge cluster:

The following descriptions are in order 1-12 per the cluster connector:

1. 18 AWG black & white: For alternator. This wire runs down to the fuse box.

2. 20 AWG tan: For brake warning lamp. There are two tan wires on the #2 connector point. One wire runs to the ignition switch and the other down to the fuse box.

3. 20 AWG pink: For fuel gauge feed. This wire runs down to the fuse box.

4. 20 AWG tan: For fuel gauge. This wire runs down to the fuse box.

5. N/A

6. 20 AWG dark green: For temperature gauge. This wire runs down to the fuse box.

7. 18 black: For ground. A clip on the end slides into the sheet metal behind the bottom RH (TS) corner of the gauge cluster panel. It's positioned to the RH (TS) of the hole located on the sheet metal.

8. 20 AWG gray: There are two gray wires on the #8 connector. One runs to the RH heater lamp. The other is for the cluster lamp, which runs down to the fuse box.

9. 20 AWG dark blue: For RH signal lamp. This wire runs to the turn signal connector.

10. 20 AWG light blue: For LH signal lamp. This wire runs to the turn signal connector.

11. 20 AWG light green: For dimmer switch. This wire runs down to the fuse box.

12. 18 AWG black (Perhaps black and brown): This wire runs down to the fuse box. Apparently this wire routes from the firewall block to a "4 amp inline fuse", and then onto the junction block.


More simple. I believe Vette made this up. It's varified: