Our 95 park ave ultra with 70k is experiencing drastic voltage fluctuations. They are intermittent and cause all the lights to dim the heater/ac fan to slow down etc. When it occurs at idle the car runs real rough. I have taken it to the dealer who recommended the alternator and battery be changed. I have done this but the symptoms still exist. It does not have any trouble starting even down to zero degrees. I used NAPA brand parts for replacements. Help!

Corroded battery cables can be a culprit too.

I am going to try that tonight. Thanks.

Update - the voltage fluctuation occurs when the headlights are on. Today I had no problem with the voltage during the daylight hours. Changed the ground cable and it appears tone better. Had to order the positive cable. Will update as soon as I complete the cable change.

Thank you for keeping us updated.

I agree with Mike, under a larger load the cables are able to deliver the current. Kind of like a clogged water pipe, it can trickle water, but when the faucet is wide open, it can't increase the water flow. Bad/ coroded cables and marginal grounds are can show proper voltage, but inability to deliver required amps.

Not a probable culprit for your issue- a slipping alternate belt will reduce the ability to regenerate amps and deliver ample current. I learned that in 1980 on my 1971 ElCamino, while in high school.

Just replaced all the battery cables and the problem is gone. Battery voltage is around 14 steady instead ofmthem15 to 8 fluctuations.

Outstanding! Glad you got her fixed!

I have a 1995 Buick Park Avenue with 143000 miles. I've replaced starter, alternator, battery cables, still voltage gauge will drop to about 10 and come back to about 13 with everything off. Also as the temperature increases, the voltage gauge drops back to around 12. The cooler the temp is, the stronger the voltage. Any ideas on locating all grounds for this car?

did u have the battery load tested or try a different one?