You don't need all of these, but it certainly helps to have a engine temp meter when your cruising down the road.
* Electrical voltmeters monitor your vehicle's electrical system. The voltmeter is accurately considered superior because it is much less tricky to wire. The ammeter requires all of your systems output to be driven through it via heavy gauge wire, while a voltmeter only needs to tap into the circuit.
*manual transmission vehicle or you are a speed demon that pushes your car to the red line.
* A fuel/air ratio gauge allows you to monitor how much gas and air is reaching the combustion chamber. If your fuel mixture is off, the engine will not run properly.
*oil pressure drops, you might have an oil leak or a faulty pump.
