When I got my newest EV, it only had one operational gauge in the instrument panel - the speedometer. The other gauges - tachometer, fuel gauge, and temperature gauge - just sat there, pegged to the lowest reading. I suppose they don't really need to work, as the Electricar had been driven over 25,000 miles without them. However, I find that driving around with dead instruments is somewhat annoying.
I found a group in Australia that makes a small device which turns the fuel gauge into a state-of-charge (SoC) gauge, and the tachometer into an ammeter. It also incorporates a system to light up a LED when the pack reaches a certain low level, mimicking the low fuel light in many vehicles. The adapter is called a ZEVA Fuel Gauge Driver Plus.
Here's a picture of all the gauges working - even the temp gauge. I bought a temperature sender for the original ICE engine - about $10 - and attached it to the motor case. The temp gauge is working, but the motor just isn't hot enough after 13 miles to make the needle move much - probably about 80f in the picture below. I drove for 30 miles on the freeway the other day, and the needle moved towards the higher end of the 'normal' range. Actual temp of the case was about 140f at that point.
The fuel gauge is fairly rudimentary, but is much easier to figure than a 'wagging finger' volt meter, and doesn't need another instrument box attached cattywompus to the dashboard.
I have the tach/ammeter set for 8-cylinder mode. 2,000 RPM = 100 amps.