When you think about the number of sensors that your engine has, it seems like there is an endless amount of gauges that can be installed to monitor their readings. Some of these readings are important, but many of them are simple inputs to the vehicle's computer. The most common gauges on today's vehicles are the speedometer, tachometer, fuel gauge, and temperature gauge. Besides having these gauges, your car will have a number of warning lights that will illuminate if there are problems with those systems. One gauge that is missing in most vehicles is the charging, or voltage, gauge. With a little information you can easily add a voltage gauge to your vehicle. Most vehicles built today come with a warning light on the dash that looks like a battery.