Dash voltage gauge acting up

[oceanworker]

my dashboard voltmeter on my 91 sport is sweeping back and forth while I drive. Any ideas? Is my alternator acting up or is it a back gauge.

 

[Ronin8002]

Does it do this only when you're driving or always whenever the engine is running? Try measuring the voltage at the battery to see if your voltage is flipping up and down. I had a similar problem and it wasn't really that my voltage needle was "sweeping"...it was just dancing around a little when I was idling. It was due to my battery cables starting to go bad.

 

[oceanworker]

Key on, engine off it acts normal. Once I start it at idle it sweeps back and forth between about 8 and 14 and when driving. A volt reading on the battery is normal. Is the gauge reading off the battery or the alternator output?

 

[tac0meat]

mine does it too when idling, it just swings back and forth really fast, i can even see my headlights and interior lights flicker a little with it

 

[Ronin8002]

hmmm...you may try measuring the voltage at the alternator....there's a little plastic cap that covers a nut with a wire going to it....that is a positive wire connection....then use anywhere on the engine block or chassis as a ground. If voltage is jumping around on the reading you get there, it could be the voltage regulator or the alternator.....seems weird that your battery voltage was normal though....are you sure the voltage at the battery wasn't fluctuating?

 

[Opera House]

Could be

a bad gound cable from engine block to frame. Remember the alternator references voltage to the engine block and the voltmter references it to the frame.