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TOPIC: 1980 5 speed electrical issue

1980 5 speed electrical issue 18 Jul 2012 12:52 #9808


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I have a 1980 5 speed and I recently got the a/c working. I notice that when the a/c runs it tends to drag the battery down. I drove the car a few miles on the highway with the a/c on; when the a/c is on and the car is at speed the voltage is just below 12 volts. After I got off the highway I shut the a/c off to see how the electrical system would respond. Voltage seemed to recover and would slowly get higher. When I stopped at a light voltage would drop to near 10 volts when the car was idling. When I was at speed voltage would return to near 12 volts. After a while voltage would continue to build to near 13 volts (where it is normally).

I keep the battery well charged; when I do not use the a/c the electrical system seems to perform just fine. I am wondering if I have a weak battery and should replace it or if the voltage regulator isn’t doing its job and cannot hack it when the a/c runs. I assume on this car the voltage regulator is integral to the alternator. Looking for opinions… should I replace the alternator or battery or is there another cause for this situation? Welcome any comments.

Thanks,

Glenn
Glenn Simpson
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1980 5 speed electrical issue 18 Jul 2012 19:35 #9822


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GlennS;10102 wrote:
I have a 1980 5 speed and I recently got the a/c working. I notice that when the a/c runs it tends to drag the battery down. I drove the car a few miles on the highway with the a/c on; when the a/c is on and the car is at speed the voltage is just below 12 volts. After I got off the highway I shut the a/c off to see how the electrical system would respond. Voltage seemed to recover and would slowly get higher. When I stopped at a light voltage would drop to near 10 volts when the car was idling. When I was at speed voltage would return to near 12 volts. After a while voltage would continue to build to near 13 volts (where it is normally).

I keep the battery well charged; when I do not use the a/c the electrical system seems to perform just fine. I am wondering if I have a weak battery and should replace it or if the voltage regulator isn’t doing its job and cannot hack it when the a/c runs. I assume on this car the voltage regulator is integral to the alternator. Looking for opinions… should I replace the alternator or battery or is there another cause for this situation? Welcome any comments.

Thanks,

Glenn

I'd check the ground cable and ground points first... Easy to do, a frequent issues and cheap to fix. Do you have trouble starting the car (i.e. slow cranking)?
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1980 5 speed electrical issue 18 Jul 2012 20:47 #9823


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Martin,

I don't usually have have problems starting the car. Is there a diagram that shows all the grounding points on the car? Or is there some other reference I can use to make sure I get them all?

Thanks,

Glenn
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1980 5 speed electrical issue 19 Jul 2012 18:52 #9834


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Glenn, I would not rely on the dash mounted volt meter. Get it checked to be sure what is going on. It just may be time to rebuild the alternator. You could have diodes going bad or something.
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1980 5 speed electrical issue 19 Jul 2012 20:12 #9835


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OK; so far it seems the best couse of action is to check the grounds if they are ok then go after the alternator.
Glenn Simpson
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1980 5 speed electrical issue 20 Jul 2012 02:22 #9839


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I would suggest checking voltage at the battery *when* the voltage is showing low.

In my '90 GT, I have seen the voltage drop to zero on the dash gauge, but when I checked voltage at the battery it was still being charged. So apparently I have a dash gauge issue (or wiring related to it).
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1980 5 speed electrical issue 20 Jul 2012 15:27 #9841


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Read this to help diag batter drain.
the link is in our tips section
http://forums.928oc.org/vbulletin/showthread.php?t=864

and another good step by step on cleaning 928 GROUNDS with pictures

http://forums.pelicanparts.com/porsche-928-technical-forum/586148-ground-cleaning-16v-euro.html

plus one more

http://forums.rennlist.com/rennforums/2220328-post33.html
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1980 5 speed electrical issue 24 Jul 2012 15:58 #9873


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Stan, Brad,

Thanks for the advice. Brad lots of helpful instructions and pictures; it will take a while but I will work through it.

Glenn
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1980 5 speed electrical issue 25 Jul 2012 01:06 #9876


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Let us know how its going as you complete each step.

You should document it in your car profile page.

Brad
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1980 5 speed electrical issue 28 Jul 2012 11:50 #9893


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OK. Will do.
Glenn Simpson
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1980 5 speed electrical issue 16 Aug 2012 08:41 #10202


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First thing to check is the alternator belt - it should be really tight and unworn. If the V-belt on the older cars touches the bottom of the pulley groove, it is worn out.
Wally Plumley
928 Specialists
www.928gt.com
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1980 5 speed electrical issue 17 Aug 2012 03:46 #10232


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These cluster gauges simply aren't usually too trustworthy. As others have said, check your voltage with a multimeter when the gauge seems inaccurate. You'll likely find that it is charging correctly though the gauge is indicating a low charge.
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1980 5 speed electrical issue 20 Aug 2012 22:07 #10326


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That makes sense. I will try that after I finish fixing my passenger side window.
Glenn Simpson
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