Alternator / Battery re-charging Woes

[Groovy911SC]

My battery will not re-charge. The battery (new) has been tested at Interstate Batteries and it tested fine. The alternator has been rebuilt and re-installed in my car. The engine has been recently re-built (by me) and runs well except for the battery not re-charging issue. I've replaced the battery, re-built the alternator.
When the engine is off, the battery reads on my multi-meter at 12.6 volts. When the engine and RPM level is around 2000 the volts read 12.50. If you wait a few minutes the reading for volts changes 12.46, then 12.40 over say 3 min until it goes way down.

Here are some clues that are starting to confuse me. When disassembling the engine/alternator fan housing, I noticed the thick ground wire that goes to the case was NOT connected to the case. Here is a picture.

You can barely tell that is the wire since all the grease is all collected on the connector end. It is not connected and looks like it was run that way for a long time.
If it was run like that why did the car seem to work fine? Weird.

Another confusing part to this is sometimes a voltage regulator will go bad causing the battery to over charge and cause problems. When I went looking for the voltage regulator, I could not find it. I thought it would be here...

I thought it would be to the right of the heater relay. Could it be in another location?
My car was manufactured in March of 1980. I thought these cars had external voltage regulators. Could it be my alternator is a later unit and I didn't know any better?
Could I have connected the alternator incorrectly?
I'm not skilled at sorting out electrical issues but I need to learn the basic etc. I have Waynes 101 project book and the Bentley Manual for my car 1980 911SC. I also have the factory manuals.


If anyone has any troubleshooting tips I would certainly appreciate hearing about them and hearing about similar issues!
Thanks in advance!

[Nitrometano]

Check all the alternator cables. Check is the thick red cable have 12v all the time. Check if the thin blue cable is conected to the small positive terminal, this is the idiot light cable. Check is the thin brown wire is conected to the small negative terminal in the side of the negative diodes. The other thick brown cable is conected in the housing side and the engine block side. I cant remember if the 1980 alternator have a external voltage regulator. I put a 1984 alternator with internal regulator to upgrade the 55 amp alternator in a 1972 911 and to replace the 75 amp alternator in a 1977 911 with a fan housing modification.
No more alternator problems since that.

Check the manual for another tests.
Good luck!!

[ruf-porsche]

Does the charge light come on before you start the engine? If not, that is your problem, you have a bad blub. The charge light is part of the circuit for the charging system, no charge light, no charging.

Your alternator should have a built in regulator. The regulator is part of the brush assembly with the alternator.

[304065]

A search here using the words "D+/61" will turn up a mother lode of good info.

You DO have an externally regulated car: I can see the plug for your old voltage regulator. Someone has converted to an internal regulated version. As long as the brown wire (D-) was connected, everything would seem to work fine, until it failed from carrying all the load. Think of it like this: the Carrera alternator puts out 1260 watts, or 90 amps. The POSITIVE component of that load goes through the fat wire to your starter. The NEGATIVE component has to come through the ground wire, which is why it's a fat braided strap. It can still make it out of the alternator, over to the 14-pin connector through the small brown wire, but eventually, that will fail under a 90 amp load, such as if your battery was drained and you started the car anyway.

I would expect to see some melted wires going to the alt. Be sure to disconnect the battery before removing the alternator: the B+ wire is hot all the time, regardless of the position of the ignition switch, and will act like an arc welder if it touches the engine block. . . be careful!

[Groovy911SC]

Here is an update as to what I've done so far. I had my original alternator rebuilt after I rebuilt my engine (the electrical worked fine before I had my engine problems) With the rebuilt unit back in the car, the voltage at the battery was 12.3volts with engine running. Bought new rebuilt alternator from shop in Ca., put the unit in the car and same result, 12.3 volts at battery but, the red light on the gauge with the druck oil pressure lit up (has a "G" under the light) and has not gone out. okay, so I thought bad ground somewhere. I replaced the ground strap at engine transmission (new) and the ground line that goes to the chassis at the battery (new). Same result! What I have now noticed is that the battery area, on the side next to the wheel well has a good bit of rust. The rust has eaten through near where the small rubber line for the window washer comes through the wheel well. This is very close to the mounting bolt for the ground off the battery. Can an excessive amount of rust be the culprit? Can the rusted area break the circuit and not allow the battery to recharge?

[lonewolf]

you need a ground strap from the back of the fan housing to the crankcase.
check also to make sure you have a ground strap from the regulator panel to the ground stud to the right of the panel.

[Groovy911SC]

Thankyou Lonewolf!

[lonewolf]

911 s run best at 14.0-14.5

[pauls81sc]

Originally posted by ruf-porsche
Does the charge light come on before you start the engine? If not, that is your problem, you have a bad blub. The charge light is part of the circuit for the charging system, no charge light, no charging.

This was exaclty the problem I just had.

[HardDrive]

There is a copper disk that the brushes, including those for the voltage regulator, contact with in the alternator. This disk is quite thin, and can provide a poor surface if not replaced. Was that included in your rebuild?

[Groovy911SC]

HardDrive the disk was replaced so says the tech who did the work locally. I don't know about the one I purchased in Ca, which is the one in the car.

[Groovy911SC]

I moved the ground for the battery to another location on the chassis. Same result. I'm beginning to think it is the internal voltage regulator. The alternator is a Paris-Rhone 14V 75A A 14 N 11. Part number 911 903 120 04.

The voltage regulator is an aluminium part with ribs a two hex bolts holding it in place?

[Groovy911SC]

At my wits end here... Replaced the internal voltage regulator, still 12.3 volts at battery at idle. Reg (G) light never goes off. Gotta be the alternator. Could I have a bad line from the alternator to the battery?

[Groovy911SC]

Well... I had the starter wires reversed. Connected the starter correctly and getting 13.5 volts at battery. I feel kinda silly.

[vash]

glad you found it. you did install a ground wire from the back of the alt to the engine block right?

[Groovy911SC]

Yes, I actually installed all new ground wires for safe measure during the engine re-build. The wire swap on the starter is one of the simple things I should have looked at instead of rebuilding alt, new voltage reg, new ground straps.... live and learn!!!