Fuel gauge bounces, cluster ground?

[mpv86dually]

1986 Suburban c20
I thought at first may just be a cluster grounding issue. First off, when turning on the turn signal the Fuel gauge jerks in unison with the turn signals. It is worse if the lights are on. I was thinking ground issue. Pulled the gauge cluster out and didn't see any direct grounds other than the wires in the cluster harness. However I did find a curious wire that seems to lead to nowhere. On the back of the upper right bulb (facing the cluster from front) There is a terminal that has a lead on it that connects to a nylon insert just above the ash tray, no obvious metal to metal contact anywhere. I don't see this in any schematic (or I just can't find it). end that is circled snaps in the dash above the ashtray.

Thanks,
Mark

 

[mpv86dually]

Well I figured out what that "wire" is. It is not a wire. It is a fiber optic thread that takes light from that bulb and illuminates the astray, when it works, that light end was not in the socket correctly ad is now. However that doesn't help by bouncing fuel gauge.

 

[chengny]

Since the cluster is still out, carefully check the clips that the gauge's terminal posts snap into.

First, check that the "tulips" of each clip are clean where they contact the gauge terminal posts. Check for tightness as well - if necessary, they can be bent inward a bit to regain their original clamping force.

Another contact point that can loosen up over time - and is often overlooked - where the "ears" at the base of the clip interface with the printed circuit. Squeeze each clip and push it out through the cluster bucket. Check the point of contact on each ear and clean with fine emery if necessary. If the clip ears were dirty enough to need cleaning, it's a safe bet that the corresponding area of the etched conductor - on the printed circuit - will need it too. For that, use a pencil eraser to gently remove any deposits.

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Having said all that, keep in mind that just because the gauge is bouncing, doesn't necessarily mean that the problem is local to the instrument panel. It could be anywhere in the fuel gauge circuit - or it could be a ground issue in one of the exterior lighting circuits (probably parking/directional lights).

If cleaning/tightening the gauge connection to the printed circuit doesn't help, you should check:

1. The IP circuit's common ground connection at the ground bus block:

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2. The ground connection from the fuel tank sender to the frame:

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If those are clean/tight, move on to the ground points for the exterior lighting.

In the front, there are two sheet metal grounds and one to the frame:

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Most trucks have only one ground connection for the rear lighting circuits. It is generally behind the LH lamp assembly.

 

[mpv86dually]

Thanks for the details, I'll get to checking everything out an let you know.