Toyota Repair: voltage meter, volt ohm meter, strobe lights

Question
Let me start by acknowledging that I totally understand if you do not answer this because you are not listed as a "General Motors" person, but I am desperate for any advice and no one else seems to have any.  I have a 99 sonoma.  Basically, my voltage meter just continually fluctuates around 15-17 volts.  The needle never stops traveling back and forth.  All of my electronic components then become brighter and dimmer as this happens.  At night time my headlights almost look like a set of strobe lights.  My battery is new, the connections are clean.  This is awful because the truck runs great, but its almost undrivable at night because of this.  Any advice????

Answer
My best guess would be that there is an alternator problem, do you have an actual volt/ohm meter that can be connected across the battery to check the voltage there while the engine is running, if so the voltage at the battery should be about 12.8 to 14 volts, if you get voltages of more than that the alternator is overcharging and may also be causing the voltag fluctuations.