Charging Woes???

moparterror · 12-11-2003, 12:45 PM

first off i have a 79 911sc. i just put in a new alternator and regulator in, and a new battery. went for a 2hr cruise, everything was fine till about half way back home. alternator light turned on. everything started to get dim and dimmer. just when it was going to die, evrything came back on, light went off, full power. drove the rest of the way home. shut it off. went inside to get a drink. came back out to put it in the garage. started up and the light came back on. now(year later) still fighting same problem.

NEED HELP!!!!!

cowtown · 12-11-2003, 12:50 PM

I'd check voltage while not running (should be ~12-12.5V) and while running (should be 14-14.5V).

If it's not charging, check all grounds first, then begin suspecting that there is a problem with the VR, then the alternator.

If charging is intermittant, I'd suspect an intermittant grounding connection first. Did you try to clean up all the connectors when you replaced the alt.?

Good luck!

corey79sc · 12-11-2003, 01:00 PM

this is my real user id, mine wasn't activated yet.

were do i find all the grounds at on my car

earossi · 12-11-2003, 01:05 PM

One of the Achilles heel items for any old Porsche is a loss in ground continuity. There are multiple grounding wires/straps in your car, and the loss of any one or more of those grounds due to an increase in resistance will produce the effects you have seen.

You should be looking for ground attachments that show a great deal of oxidation and/or rust. You may also have a ground that has fatigued and broken........meaning that as the car vibrates, the ground can open or close.

That would be my first approach. You may need to do a test where you run a hardwire from the alternator body to the negative terminal on your battery........if doing this shuts off your light, then you have the answer.

Lastlly, look at the VR that came with your alternator. You should be able to replace the VR and brushs as one unit. Have never priced them for a Porsche.....but, other Bosch alternators usually can be refitted with a new VR for about $50.

Have you also checked for looseness in the negative terminal on the battery? That can produce the loss of ground mentioned above as well.

304065 · 12-11-2003, 01:10 PM

Please check the archives using the search function for this, there are about 40 recent threads describing exactly the same problem. There was no internal VR until 82.

surflvr911sc · surflvr911sc's Garage

Don't forget to check the 14 pin connector too.

corey79sc · 12-11-2003, 01:39 PM

ok here is what i have done. i went and got a battery today it is good.
when i start the car it is not charging at all. the light in the dash does not come on when it is runing but when i turn the key on it does come on.
adn it does come on when i turn it off. the 14 pin is were???????

corey79sc · 12-11-2003, 02:03 PM

ok here is what me have done now.
we have looked at the 14 pin and it looked good cleaned the battery terminals. well i do not know how to say it but it is charging but it is not.
car off 12.5v it running is 13.8v and with the lights on 11.5v i do not know what to say

fintstone · fintstone's Garage

Corey
Not sure I understand.
When the car is is off, the light should come on. When it is running above idle, the light should go out and stay out until you turn the engine off. Where are you measureing the voltages you report..at the battery or alt.?

corey79sc · 12-11-2003, 02:29 PM

at the battery

corey79sc · 12-11-2003, 02:33 PM

if the alt. is not charging will the light come on?

fintstone · fintstone's Garage

You should have a red wire that goes from the alternator to the starter. At the starter, it should attach at the same place as a black wire that goes to the positive battery terminal. This is your B+ charging voltage. Check these connections. If good, check the brown wires from your alt and regulator. They are the grounds. Make sure they are clean and grounded. Finally, check the connections between the alternator and regulator. Unless you have upgraded to an internal regulator (attached to the alternator), you should have a blue and a black wire between these. Assuming your regulator is good, based on your description, I would suspect the black one has a bad connection if the brown wire from the regulator you checked earlier was a good connection to ground. Since your battery is new, If these wires are all good, I would suspect a bad regulator. Good luck. Let us know!

fintstone · fintstone's Garage

Corey
When you turn the key to on, the alt light comes on. If you turn the key to start and start the car, it stays on until your charging system puts out over 12v..it should go off at speeds engine speeds over about 1500 rpm. When you switch your car off, the light should not come on.

corey79sc · 12-11-2003, 03:15 PM

yes it works just like that. but i was looking that the wires by my regulator brown is a good ground. what is the little box that it goes in befor the the reg. and can i by pass it and just go from the alt to the reg with out the little box

fintstone · fintstone's Garage

I am not sure what you refer to. are you tallking about the brown wires going into a box? ?is it a terminal block? are there 2 or three brown wires there?

corey79sc · 12-11-2003, 03:35 PM

ok there is a harness from the alternator to a little black box and then into the VR.
into the little black box there are a brown, black, blue wire. then into the VR there are red, brown, black. what is this black box for. can it be bypassed?

fintstone · fintstone's Garage

I cant picture this part. I don't have an SC to look at...only wiring diagrams. Sounds like either noise supression or a terminal block. Are you sure the alternator wires go there? Is there a part number on it?

corey79sc · 12-11-2003, 04:47 PM

well the wires went into the box then jumped up to the regulator. we bypassed the box and nothing changes. no part numbers that i could see.

Wil Ferch · 12-12-2003, 11:21 AM

Wait...we're getting off track.
A fully charged battery when the car is "off" should read 12.6 volts. When you turn the ignition to "on" , but have not turned further to start the car...the charge indicator light should come on. If it doesn't , and the light bulb is found to be burned out....the alternator won't charge properly ! If you turn the starter switch fully to "start", the light should go off as soon as the motor is running and spinning.
At idle....the voltage at the battery shoulf now be 13.2 + volts. If you now rev up to 2000-3000 rpm, it shoulf be closer to 14.2-14.4 volts. If the high value is over 14.4....bad regulator, usually. If it is under 12, ...also a bad regulator or it can be a bad alternator. To check, compare the voltage with lights and accessories "off" ...and then "on. Under load...the normal ( load off)14.4 volts may drop to 13.2- 13.8 (load "on"). If the voltage is too low, like 11.9 or so... and it *doesn't* change when the load is on or off....it's a bad alternator. If the load under these conditions *does* change ...it's a bad voltage regulator ( hope these last two points isn't reveresed !!).
---Wil Ferch

corey79sc · 12-12-2003, 02:07 PM

i am thinking it is a bad regulator. it is working right when it is running it is at 13.5 like you said but under a load (lights on) it will drop to 12.0 or 11.5 not good. do you know a way to test it out of the car.
thanx a lot for all the help
i know we will get this one
corey