I just had alternator rebuilt and new regulator installed. The guages say 12 volts and drop when blinker comes on. Have A/C and radio on as well. Is the guages bad or are they telling me something. I will test with voltmeter shortly.
But, can poor grounds cause this as well.

 

If poor grounds were a sauce they would be ketchup, nothing they can't do.

If the pod gauge doesn't match the jump post with a real meter, almost 100% its a connector or ground issue.

 

Thats sig material right there.

 

So where should I start checking the grounds and how do you check the grounds

 

Actually your car sounds ok, I wouldn't worry.

Eventually you should find and perform Wallyp's annual pm, which I think includes a diagram showing all 9 or so ground points.

 

Where do I find Wally P's PM. I have time this week so let me get it done.

 

I recently thought my alternator was failing because the voltage indicator on my radar detector was showing 11.5 volts where it always showed 13.5 before and the car would sometimes die at idle.
I found a large red cable at the jump post that had moved and was touching a bolt on the brace nearby. It wasn't arcing, at least that you could see, and didn't have any sign of carbon on the insulation but the insulation did get worn a bit at that point. Once I moved the cable off the bolt the voltage went back to normal.

Just another gremlin to look out for....

 

Grounds:

https://rennlist.com/forums/928-foru...ons-chart.html

Wally's PM is listed in a thread you started 2 summers ago, the last time you had a grounds problem

https://rennlist.com/forums/928-foru...ard-start.html

 

Yep and saved this in my folder. Taking it out and doing the maintance today. Hey I am getting older and forgetting more. That is why I go here to get the answers.

 

Well mine goes below 12 when headlights, driving lights and AC is all on at idle, but never into the "red" so to speak. I noticed 100% difference when I changed my alternator belt out for a new one and tightened it up.

 

Not sure about you 84 but on the early 928's there are 8 connections between the battery and the guage. A build up of corrosion on any of these connections can result in lower gauge readings. Also, Porsche used a common circuit for the gauge so any other draw (brakes, turnsignals, etc) can skow as a drop in voltage at the gauge. Checking the grounds and cleaning any corrosion off the instument panel fuses may fix the low reading. Also, check the positive battery cable connection at the starter and connections on the jump post.

Dennis

 

I cleaned the ground conections at battery and frame to motor. Noticed a change in the gauge reading. Then after about 5-7 minutes, the guage dropped. It is not as bad as before, but at an idle with A/C, and lites on the guage goes down to 10 volts. What am I missing here. Is there something that cuts the charge from the alternator off. I did put a voltmeter on it and it reads 13.5 and dropped to about 13 or there abouts under load. Help, I am about to have a breakdown.

 

Your meter was 13 to 13.5 on the post and battery which is good. In the dash pod you may have a connection that is dirty, it uses a resistor to energize the alternator at low Rpm. After cleaning up my contacts gauge is now correct. I put the gauge on the bench with a power supply and it was spot on, just low when connected to wiring harness. There is an adjustment pot but you need to check the gauge first you will find its most likely accurate. Clean all your grounds including the 14 Pin post near the main power post. Every gremlin I have had has been grounds or dirty connections. If your battery is charging your good but not good enough.

 

OK, that settles it. When can I bring my 84 by to have you spruce up the electrical system.

 

When you bring your motor over !