Either a bad ground to the guage itself or a bad voltage regulator in the alternator. While the enigine is running check the voltage at the battery it should be around 13.5volts if it constantly fluctuates then the voltage regulator is probably bad. Replace the alternator. Otherwise make sure your grounds are good.
The voltage gauge on the Blazer is not the most accurate (cheap) When using the signals the voltage draw on the system is enough to make the gauge move slightly.
Electrical connection issue.
it would cause a certain lamp to be going on and off. (flickering )
I think the cause of ripple voltage would be from a bad ground or capacitve voltage.
bad voltage krunkbobulator
The battery gauge in a vehicle will move when you use your power mirrors as your causing a small drain on the battery & lowering the voltage slightly. The effect is normally only really visible when the engine is not running.
A common cause for a gas gauge to stop working in a 1994 Ford Aspire is a defective fuel gauge. Lose wiring in the dash is another cause.
Defective voltage regulator.
Well, kinda need to know if it did anything else. If the vehicle continued operating at normal, probably a fault voltage gauge or regulator. If you actually lost all power, the whole thing would shut down. If it was a temporary loss of power, then it kicked back to normal, you're probably looking at a loose or faulty ground wire.
Bad voltage regulator
A potential bad gauge or sender unit in the tank would cause it to read full all the time.
Have the alterntor and voltage regulator checked.