Darinm

Not sure if this is anything to worry about or just one of those annoyances that i'll be living with. I noticed this week that my volt meter will jump occasionally (like every 20-30 seconds). It typically stays around 13 volts but will drop and go back to the same output, very quickly. My battery is staying charged and it doesn't make any difference if the lights are on, or any other electrical draw.

Is this something to be concerned about ?

MelWff

Just to be safe check the connections on the alternator. Make sure the large red wire connection is tight and unplug the two wire connector, look for any corrosion, and plug it back in.

Darinm

Yessir, did that and confirmed other connections to battery, starter etc. Everywhere there is a large wire connection. All clean and tight.

MelWff

How old is the battery and if not a sealed battery can you check the acid level?

BlowAMouse

Unfortunately you may have to look at the gauge itself.
One test that my help, if you can recreate the issue with the car idling in the driveway, hook a voltmeter up to the battery and see if that jumps too. If not, the gauge may have an issue.

mrvette

OP, when you say you checked bat wiring....did you go under the bat compartment to the frame under there, and clean/shiny metal/steel and bright metal from the negative to the frame there, and secure with a good solid bolt?? and then on the right side from the engine to up/under the engine mount horn from the frame?? do the same.....

Then, clean them sanitary from any and ALL grease/oil, and use RTV black to cover the connection but GOOD.....preclude any corrosion/rust bad connections on down the road.....

BlackC3vette

So if the lights are on when the voltage drops, do the lights flicker? If it was a ground connection, I would thinks you would see more than the voltmeter needle go down. I think I would have the alternator tested, especially looking at ripple output (rectifier-diodes). Anyway, it's a starting point.

7T1vette

Either the voltage regulator is going out in your alternator, there is some problem with wiring, or the gauge connections are loose/defective. Easiest way to determine which is to put a multimeter on DC Volts setting and wire it up to the battery connections and compare readings between car gauge and meter. Also, connect multi-meter to alternator output then drive and compare gauge and meter.

The results of those tests will tell you what direction to go to resolve your problem.

Blue73Shark

I had the same problem on my 73 (amp meter) and it turned out to be both issues described by 7T1vette. Rebuilt the alternator (NAPA kit replacing the voltage regulator) and cleaned/tightened the contacts on the alternator and the wires attaching to it via the black plug. Problem solved.
Fran

Tooch1

I also agree with Fran and 7T1 in that you should check the alternator wiring and voltage regulator. When my voltage meter went bad my volt meter started to jump and also my interior lights flickered with the gauge. A simple quick test to check if it is the voltage regulator is to just unplug the plastic wire connection on the top of the alternator and see if the pulsating meter and interior lights stop, if so, it's the voltage regulator which is located inside the alternator. Here's what they look like.
Hope this helps,
Tooch
PS- Don't drive the car with that unplugged! It's just a quick test that my mechanic told me about...

henrikse

Put a meter across battery terminals and when the voltmeter does this look at meter and see if it mimics? May need some jumpers to get it on seat where you can see it. It should be an analog meter. Does tapping the voltmeter cause this? as connection could be loose on back.