OK...long shot...
Just been over in South Africa on holiday and my dad has a South African built LN51 petrol hilux and both temp & fuel gauges are not working correctly. Have found the issue to be the gauge voltage regulator, which is integrated with the fuel gauge (it provides 7v to both the fuel and temp gauges)
Anyone have either a fuel gauge with voltage reg built in (will have 4 fixing nuts/terminals. The 2 fixing nut one is for the tacho dash and is different), or a known work around? Am currently looking at an aftermarket 12v-6v regulator to wire in, and bypass the existing one in the fuel gauge.

Thanks