Depending on the Jeep...
Coolant temp sensor is right there on the thermostat housing, in the very front where all the hoses come together at the top of the block... NOW, if it's an older model 4.0, pre '97, if I recall correctly, the sending unit to the temp sensor is located on the very back and top of the head, on the drivers side...
Oil pressure sending unit is located right there where the oil filter goes, if your left hand is the filter, the sending unit is where the face of your watch should be.
I don't know about the voltmeter, I assume it reads right from the alternator, as the voltage regulator is built in to it.