Temperature gauge & Fuel gauges not working correctly

Hi guys New to the forum ��
I have a 2004 GU TD42, I have had long range tanks fitted by ARB several years ago with no issues noted.
I had run out of fuel once although the fuel gauge was showing just under half a tank on the main tank but I thought nothing of it a few months later my temperature gauge was showing hot while on a short trip (unusual as it always has sat just under half on the gauge, have had the patrol since 2012) i immediately turned for home and got a mechanic to check it out as did didn't want to do the head gasket, after spending a few grand on replacing the water pump, temp gauge, radiator etc to be told by the mechanic it is still indicating the temp is high must be an electrical fault!!!
The temp gauge is always on high reading and my main tank level will not drop below full (even though it’s not) and therefore I cannot use my full sub tank to run on as this feeds through to the main tank which showing is full will not engage sub tank contents!

Has anyone had the same issues with the fuel & temp gauges (are they connected?) seems strange they both started playing up around the same time ��
Cheers in advance Nudger ��

The mechanic is probably correct.

I had an issue years ago where running the driving lights caused both fuel gauges to drop to empty.
If the camper was connected the main tank refused to show higher than 3/4 full.
Turned out to be a bad earth at the Anderson plug at the rear of the car....go figure....

It's common for Patrols to have multiple earths added around the car.
I'd start by checking all existing earth connections, and add a couple of extras near the main and sub tanks (Google is your friend).
Dodgy connections or gunge at the trailer plug have also been known to cause some strange electrical issues.

Fuel and temp gauges are connected.....by earth....