Fuel Gauge Issue - 454 TBI

[Evil Trailblazer SS]

Yesterday the fuel gauge was working perfectly, I drive home and shut the truck down. When I went out a couple hours later, the fuel gauge pegs way past the full line. All the way to the 3 o'clock position.

Now, I figured out a weird thing is happening with it. When I turn the ignition on but don't start the engine, the gauge reads dead empty, whenever the pumps are running (fuel relay engaged) the gauge pegs out to the 3 o'clock position. This is happening with both fuel tanks, not just one of them.

According to the diagram of my fuel pump/switch/relay/valve system, the gauge gets it's signal from the fuel tank selector valve (Pink wire), is my problem a failing selector valve? How do I test this out to confirm?


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