FUEL Gauge

My best guess is this is not a rte or any solid state regulator but just a OEM mechanical limiter. Wild needle swings are a symptom of failing mechanical limiters. I've seen the same needle swing in temp gauges where the panel had only the 2 gauges. The temp needle would swing to max then fall back to correct position at switch on but only after the water was hot. If there was a similar needle swing in the fuel gauge at cold start, I never saw it.