Also, I don't know if you already have an auxiliary engine temp gauge, but this along with oil pressure would be my first additions before a voltage gauge. The idiot light is OK for voltage, and the tach is actually a good early warning system as well, since it will start to jump around and even stop working when the alternator is going. When I got my Disco, the serpentine belt was installed wrong, causing it to slip on the alternator pulley and the tach displayed these symptoms. Something to watch for. As regards a temp gauge, I installed one using a 3/4 inch T in the heater hose which comes out of the intake manifold. I screwed a mechanical temp sender into this. This is actually better than taking the temp reading off of the thermostat area since the coolant entering the heater through this hose is the hottest in the motor, having just come through the engine. The temperature on these motors is crucial, since they are aluminum (speaking of the V8, which I assume you have) and DO NOT like to be overheated. A couple of overheats and you are looking at head gaskets at the very least. Look to keep your temp below 220 at all times. The factory gauge is really just an idiot light, and when it moves above the middle, it is already in the 240 range, and too late . . . These vehicles have superb cooling systems when they are in good order, with a large capacity 4 row radiator, two trans coolers and an oil cooler. (You won't find many stock trucks with that kind of cooling.) If yours is running hot, look to having the radiator cleaned out and replace the fan clutch at intervals as normal maintenance, as you should all of the hoses if they look original or old. The lower radiator hose is special and not easy to find locally. Go to Expedition Exchange, a subsidiary of this site, and buy a bottle of K-Seal. This will seal any leaks in your cooling/heating system and even work on minor head gasket leaks if you should have any developing.