Ford Repair: Voltage gauge in the red, voltage gauge, voltage spikes

Question
My 94 explorer's voltage gauge is reading very high (18 volts).  When I just turn on the battery and not start the engine the gauge reads 13 or 14 volts, however when I start the car the gauge jumps to 18 and stays there for as long as I drive it.  The car seems to run fine.  I put a fluke on the battery when it was not running and it read about 13 volts.  I don't know if it is the alternator, wiring or maybe the voltage regulator. I have not done any work on the electical system since I bought it two years ago. Any help would be appreciated.  Thank you.

Answer
If the voltage spikes, its the voltage regulator.  Im not sure where the regulator will be in your car, but its one of two places.  A repair manual would tell you, but if you dont have one heres where it would be. It could be on the side of the wall of the engine bay, looking like a small 2x2 inch metal box with a plug and about four wires coming out of it. If it isnt there, its on the back of the alternator and you must remove the alternator to change it.  I know that on 94 mustangs, the regulator is on the alternator so i am pretty sure yours will be too.  Although explorers are much differnt than mustangs the engines and electrical systems tend to be the same throughout all models as long as its around the same year.