I have a 2002 chevy silverado lt xtra cab 4 wd and the voltage meter will flucuate or even shake rapidily while driving and at times when all the lights, heat, accessories are on they will dim and the meter will drop below 14 then return to 14. The blinker will make the meter move back and forth when in use also. What could cause this and how do i diagnose this.

greg

 

A weak or faulty alternator. Loose connections to and from alternator. Put a volt meter on the battery with the engine running and the ready should be at 14 volts. If it is steady at 14 volts then check the battery.

 

X2. If the alternator cannot keep the voltage up with load i.e. lights ect. It either is a low output alternator or the voltage regulator in it isn't keeping up with what is required.

 

You may also want to check the ground cable, if it is corroded, check the jacket for splits or swollen portions or unusually stiff areas. the corrosion may not be at just the end of the cable.
You can run a second ground from the battery to the chassis to check if it changes the behavior of the volt meter gauge...