Gas guage twiching!

I have a 1998 Chevy K1500 Ex Cab SB Z-71 W/5.7L Auto.

-Here is my problem. My gas gauge started twiching about a year ago. It still registers the amount of fuel in the tank, but it fidgits back and forth about an 8th of an inch, maybe a 16th.

I just noticed today that when there is a load on the alternator (Like when the lights get turned off and on) it registeres a lower amount but still twitches all of the time. But it also twitches when the truck is not running with the key on. So I don't think it is an alternater issue.

* So here is the question; what is causing it to twich? Is it the fuel gauge sending unit, the gauge it-self, or a ground problem somewhere on the truck?

If it is the ground then where is it common to get a problem with it not grounding properly?

Any help or advice would be greatly appreciated!

Sorry no pics of my truck, I would like to think I have described the problem it thoughly enough!

clean all your grounds, especially the one next the the fuel tank/filler neck. The ground for the fuel tank is probably somewhere weird like up on the engine. It will be a black wire running alongside a grey wire from the tank.

Check the grounds as suggested above but my only fix in the field for this body style with this exact complaint has been to replace the sender in the tank.

EDIT: I'm a dufus. The gauge cluster is the cause I've seen. I was coRnfused but I remembered having people complain about this after a pump (reusing the sender) and the solution has been a gauge. Most people don't fix it.

That is what I was thinking, I was going to check the grounds first. I am thinking that the pump is probably going to go out soon. It has been about four years since I have replaced it. As we all know that is one of the common problems with our trucks, especially my gen of truck.

See my edit.

Now that that has been said, how likely would it be that it would be the ground connections?

-How else would I be able to change the gauge with-out changing the entire gauge cluster?
-Do they sell just the gauge?

1998 must be a weirdo year. Now that I looked at the schematic, I see it's a 5 volt and signal wire style, not a resistance to ground style most of the GMT400 trucks have. The PCM sends out 5v, the sender's resistor steps the voltage down based on fuel level, then then return (signal) circuit returns the lowered voltage back to the PCM for a reading. The PCM then sends the instrument cluster a signal on what to display. Both of the front to rear circuits pass through connector C130. This connector is a 4-wire connector on the firewall by the master cylinder (according to my information). There are grey, dark green, black, and purple/white wires. Make sure the connections on the black and purple/white wires are good.

I can't see where GM offers the gauge by itself.

I don't think that they offer it by itself. Thanks for all the information.
I will check the wire as soon as I get a chance.

What I don't get is what would cause this besides a faulty connection/wire@connection?
In my mind that would be the only thing that might allow the surges of lower/higher voltage without having it completely going dead. I would assume that is what is going on, right?

What I meant above is I looked in the GM parts computer and do not see that anything in there is offered by itself.

Not sure what causes it but it is common.

Yeah man...I would just live with it if you can't fix the prob with fixing the grounds. I had 4 different OBS trucks...and they all had fluttery gas gauges. I just learned to live with it. My truck does the same. Its no biggie. As for your fuel pump...they SHOULD last longer than 4 years. My first 2 Z71 OBS trucks never has F/P probs, but my other 2 did. I always fixed the problem by installing a Walbro unit. Much cheaper. And when you replace--either remove the bed (if a full tank of gas) or drop the tank. Either way, it ain;t that bad...