This video goes over one possible cause for an erratic (crazy spinning needle) fuel gauge for old body style (OBS) GM trucks of the 1990s from Chevrolet, GMC, Holden, & Cadillac not working. In many cases the vibrating, twitching, bouncing, fluttering, and related unexpected jumpy behavior from the gauge has nothing to do with electrical grounds or the fuel tank sender, it is simply the effect of age on the aircore motor of the gauge itself. The original internal dampening effect is lost, corrosion sets in and the aircore motor becomes unreliable and must be replaced. Note that I said “aircore motor”, there are no stepper motors in these model years. I’ve seen folks try to inject new dampening oil, silicone and such. But that is a temporary repair at best, if you’re going to open it up then do it right.
The vehicle illustrated is a 1999 Chevrolet K1500 Surburban with the 6.5L diesel engine option, but the symptoms and repair procedure apply to all GM trucks of the same general era – before the introduction of stepper motors into the instrument clusters in model year 2000.
The repair consists of replacing the original aircore motor for each gauge with a properly calibrated OEM replacement motor. These motors were never sold by GM, you have to get them from a speedometer repair shop parts supplier. They can be found on eBay (search link further below) and are an off white in color, the original yellow ones cannot be found anymore but the color is irrelevant, the motors are the same. Each gauge type uses a different aircore motor so take note of the letter codes!
If your fuel gauge was very messed up you may be in the rare situation of not being able to perform the calibration procedure outlined in the video, in that situation you will have to get access to a new fuel tank sender, hook it up and use it to calibrate the empty, 1/2, and full positions accurately. The fuel sender reports a resistance value which is what the aircore motor reflects as the gauge indicator. You can similarly re-calibrate major differences in the other gauges by replicating the source input to them.
Here’s an eBay search affiliate link for all of all of the Aircore Motor types: https://ebay.to/2YjQOd5
And one for GM part number 25089350 / ACDelco part number PC195 (replacement instrument cluster bulb) on an affiliate link at eBay: http://ebay.to/2uCn0Lm