Fixing fuel gauge, found electrical confusion

[Reggler]

So on my '72 Suburban Ambulance, the gas gauge is pegged at 3 o'clock. Reading on here says ground issue, but when I tried to ground out the gauge, that's where things get confusing. I read that you ground the wire that goes to the fuse box, where it says fuel gauge. But my truck might not have the right wires going there.
I have an orange wire that was plugged into fuel gauge on the box, that also has a pink wire piggy backed to a ground at the voltage regulator. But when tracing the orange, it goes into the headlight switch harness. Then, the cluster lights plug, has a grey wire, that has a light tan wire tapped into it also going up to the cluster but in a different harness than the cluster lights one. With both of those disconnected from the fuse box the only thing not working is the right bulb in the heater control, everything else is still functioning[aside from broken fuel gauge].


Attached are pics of the fuse box and wires that I'm dealing with. I'm trying to fix this, but it's really a struggle without pulling the whole harness apart.
BTW truck is a C10, 350/auto, No gauges, A/C, column shift. Mostly original, also aside from ambulance roof.