Another porsche with electrical problems

[PorscheAmateur]

Hello everyone, before I start off, I just wanted to mention how helpful everyone in the past has been with troubleshooting my car. Anyhow, I have a 1980 911SC that appears to have a charging problem slightly different than other threads I have read. I just recently took it to a professional garage not a month ago and everything was fine including the battery. But the other day, i took it out and that red charging light turned on. Anyhow, the car will start once the battery has been externally charged, but it appears to have something between the alternator and the battery causing the problem. What are the means of testing the charging system on my car?

[James Brown]

a quick way is to disconnect the battery and use a volt meter or multimeter to check the static voltage, then clean and hook up one cable and using a trouble light, touch the disconnected post and the other to the disconnected cable and see if it lights up, this will tell any parasitic draw is going on. connect it all back up and, using the volt meter, note the voltage again, then start the car and note the voltage. should have 12+ volts before start and 14+ volts when the alt. is working (red light out). then we will go from there.

[woland]

I had the same issue some years ago
Changed the alternator brushes and fixed the problem

[PorscheAmateur]

Ok everyone slight update, I did a drain test and it revealed NO DRAIN on the battery. Also, i did a simple alternator test by reading battery voltage with car off, during car running, and after. Results:
Before: 12.1 Volts
During: 11.9 Volts
After: 11.8-11.9 Volts

So in theory, something having to do with the charging system is screwed up. What should my next steps be?

[brads911sc]

Voltage is low. Should be over 13 running. Id say you have a bad alternator. Id take it off and have it bench tested. They can also load test your battery. Getting as much tested now will help avoid just throwing money at the problem.

[PorscheAmateur]

to my understanding, I think that the voltage is only low because i charged it off another car for a short period. Battery is 100% on everything as of last month. Any other options other than to just remove alternator and bench test. and what is bench testing?

[brads911sc]

They put it on a machine that tests it under various load levels and it takes other things like a dead cell in the battery, rpm levels, belt tension, a bad ground, etc out of the equation.. You can do this yourself with a multimeter but not as precise..

did you check your belt tension? RPM level? at 800 rpm and a loose belt you have have the same issue.

Originally Posted by PorscheAmateur

to my understanding, I think that the voltage is only low because i charged it off another car for a short period. Battery is 100% on everything as of last month. Any other options other than to just remove alternator and bench test. and what is bench testing?

[CorsePerVita]

Originally Posted by PorscheAmateur

to my understanding, I think that the voltage is only low because i charged it off another car for a short period. Battery is 100% on everything as of last month. Any other options other than to just remove alternator and bench test. and what is bench testing?

Won't matter how you charged the battery. The running voltage should always be 13+ if the alternator is charging properly.

Essentially, when the car is running at standard rpms the alternator will be charging. If the alternator is charging, you should see approximately 13+ volts at the posts, that will indicate the alternator is charging the battery. If it does not while the car is at normal RPMs, you've got an alternator that isn't working properly.

I had this issue that started to come up where the light came on sometimes. Battery tested fine, grounds were fine, it was all super great. Bad alternator.

Easy way to do this is hook up a multimeter to the battery, look at what the voltage is without the car running. Should be 12+. Turn the car on, raise the rpms to something around 1500rpm. Voltage should be 13+. If voltage isn't 13+ there's something not right (alternator).

This is not because it is a "Porsche with electrical problems" but rather, a car from 1980 that is probably the original alternator that has been run for thousands of miles and never replaced. You just end up being the lucky owner who gets to diagnose and ensure it's properly fixed.

[James Brown]

agree

[theiceman]

I cant remember if 80 has the internal or external regulator but if its external you can try swapping it with someone.
I agree however that your alternator needs to be pulled. Not difficult, just a pita

[Josh D]

Originally Posted by theiceman

I cant remember if 80 has the internal or external regulator but if its external you can try swapping it with someone.
I agree however that your alternator needs to be pulled. Not difficult, just a pita

'80 MY did have external VR, but it's possible an internal VR alternator has been installed at some point in it's lifetime as there was a Porsche technical bulletin for this.

[theiceman]

Originally Posted by Josh D

'80 MY did have external VR, but it's possible an internal VR alternator has been installed at some point in it's lifetime as there was a Porsche technical bulletin for this.

Well looking at the cost of that regulator .. if that thing ever goes I'll be up for the conversion .. may be cheaper

[PorscheAmateur]

Ok, so minor update, after looking through the 101 projects book, it says that since my charging light doesn't turn off above 2,000 rpm, that it can be due to 4 things:
1) Regulator has failed
2) Battery Lead to alternator has been disconnected (anyone have a picture showing were connection is?)
3) Alternator internal bushings are dirty or worn
4)Alternator is bad

After watching this video Auto Repair & Mechanics : How to Test a Car Voltage Regulator - YouTube I don't think that the Voltage Regulator is causing the problem because if it was the problem, the battery would show a very high charge 15+ while the car is running because the VR wouldn't be doing it's job. However I could be wrong. Next cause is a disconnected lead, anyone know where this is?

[James Brown]

you don't have a high voltage condition verified by you. doubt the alt lead to the battery is disconnected but you have to dig in there and remove most of the fan to see. best at this point is to remove the alt. and VR and take them to a shop and have it checked out.

[Tippy]

If you find the alternator is bad, have it rebuilt by a local rebuilder.

[JoeyD911]

'80 indeed did have the external, which is actually a less expensive part than the internal. Does your fasten seatbelt light happen to come on intermittently, even if the belt is fastened? No annoying buzz alarm, just the light itself is what I mean.

[SchnellSchweitz]

What part of the country do you live? I'm sure someone nearby can come lend a hand.

[speednme1]

Before you do anything, if I'm not mistaken there is a diode in the electrical circuit. If it goes bad it will give you symptoms as if you have a bad alternator. Check to make sure that isnot the case.

[dan2744]

Will a loose belt cause an overheating issue as well as an alternator issue? My 79 924 is not recharging battery and it overheated. It seemed fine before and then when I went through it thinking it was a stuck thermostat I noticed that the belt was frayed and so loose I can just pull it off with my hands.

[PorscheAmateur]

Car has been repaired. A while back, I had to jump another car using porsch. This caused the stator to break which then broke the the Alternator an regulator. I had it repaired at central jersey starter and alternator for about 400 which included removal and install.