Mechanical gauges, in the scope of a Challenger (in fact, in pretty much all modern day vehicles) have been replaced by their electronic counterparts. Is it because they are bad or inaccurate? No, not at all. In fact, mechanical gauges are extremely reliable and accurate. They are reading the pressure (as an example) straight from the source and are not relying on a sensor interface. When diagnosing engine issues, many mechanics will hook up a set of external mechanical gauges in order to confirm that what the factory OEM gauges are reading is indeed accurate.
So why switch over to electronic gauges? It is a matter of safety. Whatever fluid a mechanical gauge is set to read, that fluid is reaching the gauge itself. In the case of a mechanical fuel pressure gauge, if installed in the interior of your Challenger, this means that actual fuel will be present on the aft side of the firewall. From a safety perspective, this is highly dangerous as fuel (obviously) is a highly flammable liquid. In fact, having a mechanical fuel gauge in the interior of any car is now illegal, for this exact reason. Any type of leak or blowout would pose an immediate fire hazard and potentially a health hazard as well. Other gauges like oil pressure and coolant temperature are still allowed inside, however they pose similar health risks if the gauge and or line leaks or breaks. Hot, high pressure oil or coolant will then make a mess of the cabin and could potentially burn any occupants quite badly.
Electronic gauges are the exact opposite in terms of safety risks. No fluids actually enter the cabin. Instead, an electronic sensor measures the oil pressure (as an example) and converts it into an electronic signal that is sent to the gauge. While still fairly accurate, electronic gauges are not as reliable as a mechanical gauge. They are more complex and adding an extra sender into the equation increases the amount of things to break. Electronic senders do fail regularly or degrade in performance which leads to inaccurate readings (thus why mechanics use mechanical gauges to confirm the electronic ones). On the other hand, apart from safety, electronic gauges do allow a vast amount of data to be manipulated and displayed without taking up a lot of real estate. With three senders and three wires, you can have one gauge monitoring multiple parameters all at once.
To expand on this, there are tuning devices available on the market that provide a 4-6” touchscreen that can access all the sensor data that is monitored by the ECU, and given the fact that everything is now being run electronically, there is a lot of data. Users can organize this raw sensor data on the screen and have as many parameters as they like show at any given time. Most of this data can even be logged, charted and exported to an external computer. Oil pressure, temperature, fuel pressure, coolant temperature, transmission temperature, exhaust gas temperature, injector capacity, fuel flow etc – all of these parameters and many more can be monitored through a single digital device.