“Wandering” Fuel Gauge

[Benco]

In anticipation of getting the engine in, and also getting enough weight in the car to be able to finally tighten up various suspension bolts, the I’ve filled up the fuel tank with fresh petrol.

When I switch the car on the fuel gauge moves up to ‘full’ and then about 5 seconds later starts to drift down to about 1/2, then slowly up again. it’s not the fuel sender because that’s just sat in one position. 
 

Is this related to a tired voltage stabiliser? The voltmeter gauge is at a steady position throughout all of this.

[Escape]

The voltmeter is connected to the battery, before the voltage stabiliser. To check the stabiliser, you need to measure voltage at the output side: the light green wires that go to fuel and temp gauges. I don't think the Eclat has a signal stabiliser in the fuel sender, so the voltage stabiliser is the likely suspect.