Would a bad regulator cause a fluctuating voltage?

[93 teal terror]

I have a year old 100amp powermaster alt with a one wire hookup. 6 gage cable and a in line fuse. I replaced the voltage regulator and starter about 2 months ago. Im thinking the voltage problem started around the time I replaced the regulator.
The voltage will randomly jump from 8 to 17 volts periodically. Other times its fine. I dont have a weak battery yet so Im wondering if its just a bad guage or what. When the volts dip low the battery light will just barely come on and then flicker on and off. When it jumps to 17 volts the lights flicker brighter/dimmer. Im guessing its either a bad alt., voltage regulator or a bad ground of some sort. I've checked the wiring for the alt. several times and it seems to be fine.

 

[jrichker]

A bad regulator will cause the problem you describe. So will a bad alternator power ground.

Don’t forget the alternator power ground!!!
The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

 

[93 teal terror]

A bad regulator will cause the problem you describe. So will a bad alternator power ground.

Don’t forget the alternator power ground!!!
The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

Thanks, good info I may try a new regulator as a quick fix b/c around when this started happening is when i replaced the regulator. The ground also sounds like a good start but Ill have to wait til this weekend for that. As far as the alt. its a 2g alt. but where exactly is the battery pigtail ground? Based on the instructions and other members installs is how I have it set up now. If you think I still need a ground feel free to elaborate exactly where to run one from. I can post pics of the setup if need be
thanks

 

[jrichker]

With a stock alternator, just make sure that the secondary power ground I described in my previous post is installed & in good condition.

 

[2stangBK]

piggy back here... Sorry. Is the ground wire you speak of a copper wire with no color shield? Its actually connected from the bolt through the air injection tube on the driver side to the driver side fire wall, correct? I'm having a over voltage issue that now has apparently killed my battery.??

 

[HISSIN50]

In my experience, it can also be a loose power cable (alt to solenoid) connection.

 

[GreatWhite]

The secondary power ground looks like a flat, grey strap w/ no insulation.

 

[2stangBK]

I temp fixed the LX/DD with a borrowed takeoff alt and the battery from my GT. Seems to run fine now, however I did take a look at the ground strip and its intact and fine so I'm not sure what happened with the alternator... No time to look at it till next week and the car is gonna sit at my office all this week anyway. ..