I have a 1996 EF Fairmont Ghia and when the vehicle gets hot after working hard (towing) the voltage gauge drops below 12 volts, the oil pressure reads almost 0 and the fuel gauge drops about 2mm.
Has been doing this for the last 60000 ks so its not low on oil pressure and it goes up as soon as you turn of the air but it sometimes brings on the oil light at idle and it scares the living out of the misses.
Any ideas.

sounds like you have a earth problem
check earths under dash and at battery

Thanks for the info, got the same info from a Ford dealer.
Removed the dash cover for the central dash earth and found Ford had trapped a layer of insulating material under half the lug. Seems much better although have not done any towing.

Yeah I used to have the same problem when the fans kicked in (obviously when it got hot) and it turned out to be the fans and the headlamps shared an earth that had some grime under it. cleaned it up and no more probs.