Battery is not charging (alternator?)

[86 911]

Hi guys,

I'm stuck with a bit of an odd issue. I've searched the forums but haven't found anything super helpful for this particular situation. I have a '76 911 with a '78 SC engine. I think my alternator might be toast but wanted to ask before sinking any more money into this project. Here is a chain of events:

1. On the highway, I noticed my tachometer start jumping whenever I would use the turn signals. A few minutes later, I parked the car and then came back to turn it back on and it was completely dead. Had the car towed home.

2. I charged the battery and took the car to AutoZone. I bought a new battery as the one I had in the car before was giving some strange readings when they tested it.

3. AutoZone clerk hooks up a diagnostic computer to the new battery (now installed in the car). The battery and alternator passed the diagnostic test although the voltage regulator failed the test. On the way home, I also noticed the car was idling a lot higher than usual (related?)

4. I took the alternator out. A local shop bench tested the alternator and regulator and said both were good. Out of cautiousness, I ended up purchasing a new OEM Marchal regulator and installed it onto my alternator.

5. I put everything back together last night and started it up. Car will run for about 20 minutes and then the lights get very dim. I shut if off and battery is drained and the car won't start.

Here are some quick facts:
*Alternator light on the instrument cluster does not come on at all (confirmed that the bulb is good
*Voltage at the battery (cold) = 14.20 volts. Voltage when car is started = 13.30 volts.

Given I've replaced the regulator and the battery (and of course assuming they are both good), is the alternator really the only thing left that could be causing this headache?

[DRACO A5OG]

Whoa, 14.20v when cold? do you mean when on or before start?

I would check all the grounds especially at the chassis near gear box.

Also check the battery connectors. I was chasing a charging issue and it was my Positive side connector that had a hairline split causing havoc to the system.

[Reiver]

Buy an inexpensive voltage indicator that plugs into your cigar lighter....you can monitor the actual readings.
I'd also check all of your primary grounds and wiring to the battery/starter.

voltage cigarette lighter gauge - Bing images

[86 911]

Originally Posted by DRACO A5OG

Whoa, 14.20v when cold? do you mean when on or before start?

I would check all the grounds especially at the chassis near gear box.

Also check the battery connectors. I was chasing a charging issue and it was my Positive side connector that had a hairline split causing havoc to the system.

Hey Draco - good call on the grounds. I will check those tomorrow. The 14.20 reading was with the car stone cold and completely off. When I took the reading, the last time I started it was the day before.

Reiver - cool gadget! I will definitely be purchasing one.

[whiz05403]

I had very similar problems. Turned out to be loose wires at the starter. Cleaned and tightened and all is well.

[DRACO A5OG]

14.2v cold is not a good sign, definitely check all connectors closely, look for hairline fractures, that will certainly cause havoc to the charging system. for the grounds, clean very well and as extra measure put some di-electric grease on the out side to help prevent future corrosion, remember not on the contact side.

Strange thing is if car is on, your voltage should be crazy high if base measurements are staring at 14.3. Very strange indeed.

[Porboynz]

A good car battery usually settles at about 12.7V some hours after being charged, so anything more is very odd. The alternator will lift the battery voltage to about 13.8V - 14.2V when charging, and settle at about 13.7V when floating. You seem to be getting readings that are 1.5V higher than what you would expect to get if the alternator was not charging:
*Voltage at the battery (cold) = 14.20 volts. Voltage when car is started = 13.30 volts.*

Maybe your voltage meter is reading high? If the lights are dimming and the car will not restart then the battery is going flat. Most peculiar, good luck tracking that down, checking the battery cables, earths and starter connections, plus the engine earth strap is good to do. If the alternator passed the shops bench test and you have a new regulator then maybe the wiring to the alternator and or regulator is faulty/wrong? My quick test for a good alternator is to see if the headlights get slightly brighter when you rev the engine off idle, indicating a voltage rise.

[Targalid]

Check that the 14 pin connector in the engine bay is clean and tight. Everything that runs the engine, including the alternator and starter, goes through the 14 pin connector. The blue wire at pin 11 energizes the exciter in the alternator as well as the alternator indicator light on the dash. Big yellow wire feeds the starter solenoid. Big red wire charges the battery. You do not indicate whether you have the voltage regulator on the alternator or next to the CDI on the driver side engine bay electric panel. It is important that you have one or the other but not both. As above, you should not read 14.2 volt without the alternator charging so check your test meter for accuracy.

[Bob Kontak]

Originally Posted by DRACO A5OG

14.2v cold is not a good sign.

Strange thing is if car is on, your voltage should be crazy high if base measurements are staring at 14.3. Very strange indeed.

I have to think the v-reg would offset the high voltage in the battery and not allow it to spike higher?

As noted, 14.2 sounds suspect. Disconnect terminals and check again after you put a new battery in the multimeter. I don't believe the battery is built to deliver 14.2 volts. If it is, return it for another once MM is vetted.

[dicklague]

Originally Posted by Bob Kontak

I have to think the v-reg would offset the high voltage in the battery and not allow it to spike higher?

As noted, 14.2 sounds suspect. Disconnect terminals and check again after you put a new battery in the multimeter. I don't believe the battery is built to deliver 14.2 volts. If it is, return it for another once MM is vetted.

you are right. Battery can't be that high. 12.X vdc is max......hard to be near 13 vdc even.

[86 911]

I have an internal regulator (mounts onto the alternator) but I might also have an external one (see image - I'm guessing it's the device with what looks like masking tape on the bottom). If that's the case, I'm guessing that can't be good although I am unsure why I have not had an issue in the 13 years I have owned this car. Checking the electrical connections is on the list tomorrow.

[Bob Kontak]

Originally Posted by 86 911

I have an internal regulator (mounts onto the alternator) but I might also have an external one (see image - I'm guessing it's the device with what looks like masking tape on the bottom). If that's the case, I'm guessing that can't be good although I am unsure why I have not had an issue in the 13 years I have owned this car. Checking the electrical connections is on the list tomorrow.[/img]

Maybe new worked in tandem with the old one andold finally went kaput?

If you do find it's connected search the tech articles about how to upgrade to an internal regulator. In the instructions it should explain how to isolate the old one from the system properly.

[Targalid]

A 76 has the VR next to the CDI as shown in your photo. You say you installed a new one on the alternator? If so, the old one should be disconnected from its 3 prong connector. It is no longer used. If you disconnected the old VR in the engine compartment, then you should have also disconnected the black wire on the alternator and taped it out of the way, since it is not used for an internal VR setup. Since this problem is new, my money is still on an intermittent connection on the 14 pin connector or else a faulty ground. There are several grounds that need to be checked: the one from the alternator to the engine case behind the fan, the big one from the tranny to the body and the one from the body to the battery. Everyone cleans the negative battery cable at the battery but few clean the attachment at the body. The blue wire at 12 o'clock on the alternator is the blue wire at pin 11 in the 14 pin connector which is energized through the alternator dash light. Fiddle with these connections until you get your dash alternator light to illuminate with the ignition switch turned to run. If you cannot make it light, you may have a bad bulb. The light bulb must light for the alternator to begin charging on engine startup. When the alternator begins charging the light goes out.

[Bob Kontak]

Originally Posted by Targalid

Since this problem is new, my money is still on an intermittent connection on the 14 pin connector or else a faulty ground.

Yep.

Thread a few years back where a guy in Houston could drive his SC until it warmed up. 20 minutes or so. Summertime so it got very hot and the 12 pin connection near the left rear shock, freq valve to the Lambda box pin corroded and would separate from the female connector. Car ran like crap, poor spin up, backfiring and stumbling, etc. Classic symptoms of a bad Lambda (02) relay or blown 02 system fuse but neither was the culprit. Just a simple connection.

14 pin is easier to get to. Hope it's this simple.

[86 911]

Just got done checking everything out. Found the following:

*Inspected all grounds (battery, transmission strap, and alternator). All had strong connections also verified by my ohm reader.
*Inspected all wires at the starter and tightened connections. All checked out good.
*Cleaned the 14 pin connector and opened up the pins a bit to make sure they were giving full contact
*Found that the alternator light in the dash was burnt out - replaced that right now.

Here's what I've noticed from tonight:

1. Alternator light in the dash will not turn off even after revving the engine

2. When the car is started, revving the engine has no effect on how bright the lights get.

I'm assuming this means that the alternator is not charging the battery which points to the alternator itself being faulty. I'm guessing it's time to get it rebuilt.

Anyone recommend any shops near Los Angeles that are also affordable?

[DRACO A5OG]

I took mine to Clarks Discount Auto Parts, but have them test it in front of you. 1st time it failed second time they updated the VR. All good. Price is pretty good and life time guarantee.

Remember to take your pulley have so it can be tested, keep shims at home so they won't get lost.