I have a Brumby/Brat that has an Leone dash (for the tacho mainly, I think, I didn't put it in.) the voltmeter reads about 11.5V's most of the time (multimeter reads 13.8V off the battery), the tempmeter doesn't move from 0 unless I rev the engine alot, the oilpresure meter does the same as the tempmeter and the speedo reads higher then I'm going, which isn't too bad as I'm putting bigger tyres on it for offroad so it might get back in to the right speed. What can I do the fix the gadges reading low expet the speedo?

I would start by making sure everything is grounded properly and using sending units compatible with the gauges.