For heavily modified racing engines or f/i modified engines I can understand the need for
1) oil pressure gauge,
2) boost gauge,
3) oil temperature gauge (especially for a turbo engine)
4) and air/fuel ratio gauge
5) and maybe water temperature gauge
6) but I don't understand the need for neither voltmeter
7) nor ammeter
For a Celica with an (almost stock) N/A engine, I cannot see any need for any of the above gauges as most car comes with a water temp indicater, will let you know if oil pressure is lacking etc. Please educate me... Of course, gauges will make the interior look cool, so that is a good reason too...
And what kind of gauges do you find most useful in your car (besides what comes standard)?