73 charging problem

[rpc356]

I've searched the forum but can't find any info on this issue. Car is a stock 73.5. The other day I was out driving and noticed the voltage monitor in the cigarette lighter socket was reading too low, ~12.8V at ~3k rpm. varying rpms changed this some, but not very much. Noticed that turning on an appliance (e.g., headlights) dropped it to ~12V or even a bit lower. Then when I turned off the appliance voltage would go back up to ~13, but only for a couple minutes, then back to the ~12.8V. After a bit, the trick with cycling an appliance quit having any affect. The gen light on the dash is on when the key is on but engine off, and goes off when the engine is running. Not even a flicker at idle.

Got home and tested the alternator by unplugging the D+/61 and DF wires from the VR and plugging them together, bypassing the VR. Voltage at the battery was ~15-16V, so alternator appears to be good.

So, I says to myself, must be the VR. I ordered a replacement solid state one from our host (matches the one that was on the car), but no change. I tried bypassing the two capacitors (one on each of the D+/61 and DF circuits as shown below), but still no change. Max voltage with the VR in line is now in the 12.2-12.3 range, regardless of rpm.

The photo below shows the panel. There is one additional black wire on the D+/61 terminal of the VR that doesn't show up in my WSM wiring diagram. Not sure what that is.

Any suggestions as to where to look next?

[RWebb]

here is a compilation of tips from here & elsewhere (nice thing is your VR is separate so can be tested in situ):

Alternator & Voltage Regulator

First: - check that red light is On when key is turned & goes out when engine is running (check in darkness for very dim red light)

- check fan belt for looseness (¼”deflection, glazing, or cracking; examine pulley halves for odd wear patterns

the easiest test for belt tension is to put a big socket on the fan and turn CCW (go tighter direction, in case you're as mechanically declined as I am), tranny in neutral, of course. If the crankshaft slips, it's too loose.

DF= black wire from VR to DF terminal on the alternator. This is the "Dynamo Field" wire, it sends voltage from the VR directly to the alternator field.

D+/61, this is the "blue wire circuit."

The "blue wire" circuit is like this

Battery----> ignition switch -----> bulb holder for warning light in oil pressure gauge ----> blue wire to electrical console ---> voltage regulator ----> D+/61 terminal on alternator.

In your diagram above, REMOVE the green wires! And connect a blue wire between the IGN terminal of the Voltage Regulator and the bulb holder in the dash. Other terminal of the bulb holder goes to +12v from the ignition switch.

D- ground ok
B+ battery positive OK.

Alternator Conversion (to Internal Voltage Regulator)

Install a 68 Ohm, 5 Watt resistor directly to the warning lamp bulb holder terminals per the 4th Edition Bosch Automotive Handbook, p. 810.
- Use p/n 111-971-511 – J shaped connector

[RWebb]

Problem:

- car runs down battery while driving; Voltmeter in cig. Lighter always reads battery voltage even with engine > 3,000 rpm
- lower red light comes on with key on & engine not running; appears to go out when engine is at idle (nut checking at night shows it is actually just very, very dim and cannot be seen in daytime shade, only at night) – BUT, people have posted that on early cars, the bulb light always glows dimly and can be seen at night. Warren Hall (Early 911Sman posted: is NOT a problem, merely an indication of resistance buildup due to oxidation or corrosion in the #61 Blue wire circuit between dash lamp and field windings connection at alternator. Clean the bulb holder with a good metal polish, clean the Faston tabs, and female Faston connectors!!!

But, alternator & voltage regulator were checked & rebuilt by a local electrical shop when engine was being hotrodded ( 4k miles ago; ?? years ago)

Engine has the new style alternator with internal VR, but I did not make the change in the Porsche Tech. Bulletin to add a resistor to the existing bulb; car ran fine w/o that up until now & not sure what that does

Using the alt. light as a diagnostic tool (from Lorenfb):

1. no light with ignition "on" not running
a. bad regulator
b. bad light
c. open slip rings
d. bad brushes

2. light stays "on" with key "off" - shorted diode/diodes

3. light glows brightly while running
a. open diode/diodes
b. shorted rotor/stator winding
c. shorted alt. light wire to ground
d. bad regulator

4. light glows dimly & gets brighter with higher RPMs - voltage drop

5. light flashes at low RPMs - bad slip rings

6. light glows dimly at all RPMs
a. a voltage drop from the rear to front
b. a bad connection at the alt. B+ (need to solder the crimp connector)
c. a bad plus diode (open) will cause the alt. light to glow
d. a regulator adjusted to too high a voltage
e. excitation current from the alt. light too low (add a 50 ohm 3 watt resistor
across the light)
f. - corroded terminals at light bulb,
- pin 11 on the 14-pin connector engine wire harness ("blue wire" excitation circuit)
- oxidation around the terminals on the alternator, and
- where the fat red wire from the alt connects to the starter.
These could all cause a high-resistance connection, which is being overcome when the alternator puts out greater current at higher revolutions. The problem is, every time it revs up, it heats those high-resistance connections, making the problem worse.


7. Light doesn't come on when driving, but battery is not charging up?

a. Bad regulator
b. Voltage drop from alternator
c. Bad battery
d. Weak alternator
- a voltmeter should help locate/solve the problem.

[RWebb]

From Wayne’s 101 Book (101, Project 20, pp. 61-63) & Comments by Grady:

Alternator indicator lamp is on with the ignition key off.
Alternator has failed and diodes have shorted out.Replace alternator , and in the meantime disconnect the battery to preventing it from becoming completely discharged.

Alternator light does not come on when the key is turned on.
Alternator bulb has burned out.
Regulator has failed.
DF wire is disconnected or broken from alternator.
Alternator has failed, and internal windings are open.
Brushes worn down too far, causing intermittent contact with slip rings


Indicator light remains on after engine is started and above 2000 rpm.
Regulator has failed.
Battery lead to alternator has been disconnected.
Alternator is not firmly grounded.
Alternator internal bushings are dirty or worn.
Alternator is bad.

Indicator lamp is dim after starting and gets brighter as engine rpm increases.
Battery lead to alternator lose or bad.
Ground connections are bad.
Alternator is bad due to open diode failure.

Indicator lamp is dim after start-up and gets dimmer and goes out when rpm increases.
Low charged battery.
Poor connections to battery.

Indicator lamp is dim after start-up, and gets dimmer as engine rpm increases, but never goes out.
Regulator has failed.
Alternator is failing.


This diagnostic tree works OK if there is one problem. But often, there are multiple problems, particularly with intermittent connections or one problem causes another.

The first place to start with the diagnosis is always to clean and check all the connections.

With the often neglected transmission ground strap, there can be a problem when starting with a poor ground connection. In this situation the entire engine and transmission becomes connected to the positive battery terminal (however briefly). This can cause serious problems in other circuits, not infrequently the charging system.

A unique feature of Porsche’s charging system is the fact that the warning lamp is an integral part of the system. It isn’t simply a warning light. The wattage of the bulb is important.

[RWebb]

Testing:

1st – check the fan belt tension, cracking, glazing, etc.

2) Acess the Votage Regulator, and disconnect the blue wire at the bulb holder. Using a jumper, measure the resistance in the blue wire from the bulb holder terminal back to the D+/61 terminal on the voltage regulator. Should be close to zero ohms, anything more is a high-resistance connection somewhere.

2) Measure resistance from the blue wire at the alternator (without it connected) back to the VR. That should also be zero.

Put an ohm meter on the alternator hot output to the case. If open it's no good.

If the alternator light is always on, then you have one or more diodes in the alternator that have failed allowing current to flow as follows: From the battery positive terminal through the large black cable to the starter; through the fat red wire to the B+ terminal on the alternator, through the busted output diode into the stator, where it then flows into the "trio" diodes and out through the D+/61 terminal, through the engine wire harness to the 14-pin connector, through the electrical console to the blue wire, out of the blue wire into the bulb holder on the oil pressure gauge, through the bulb (lighting it) and then through the red wire with black stripe to the ignition switch, then to ground.
- John Cramer

1. The '82-'89 Porsche 911 alternators from Paris-Rhone are NOT reliable because of the internal regulator which gets very hot. This results in overcharging intermittently, and all the time. The use of an internal regulator in an air cooled 911 was NOT a good design.

2. The alt. light must come on with the engine not running and the key "on".
The alt. light energizes the internal regulator to allow charging when the
engine starts.

3. The light must go "out" when the engine starts. Once the engine starts, a glowing light, dimly, indicates a voltage drop (alt. to starter, starter to battery). A bright alt. light usually indicates a bad alt. diode.

4. The Paris-Rhone regulators are set for about 14.75 volts at the alt.
The voltage at the battery will usually be .50 to .75 less with min. accessories and a good battery. Note: Alt. regulators operate as switching regulators, i.e. they turn-on when alt voltage falls below at set point (A) and turn-off when they turn-off when they reach the upper set point (B).
They don't operate as a linear regulator as some may think.
The B-A voltage is the hysteresis of the regulator usually 0.50 volts.

5. The alt. battery lead must be soldered to the crimped connector or
a voltage drop will occur. Early 3.2s & SCs were NOT soldered.

6. The actual voltage at the alt. can be measured at the alt. light in the instruments on the dash.

7. The alt light & wiring can be checked by gounding the blue wire at the alt. The light should glow brightly.

8. Common alt. problems occur because many forget that wires from the rear connect to the battery in the front and can cause voltage drops with bad connections.

9. The alt. brushes should be at least 0.50 inches to a have fairly reliable alt. for 50K miles. Also, the slip rings must not be deeply grooved.

10. The alt. belt must not be overly tightened, i.e. not less than 3/8 to 1/2 in. belt movement. Also, the fan must not be forced on or the rear alt. bearing plastic support will be damaged. Remove the Alts from the fan housing using a wooden block to "shake"
the alt. from the housing, no hammers please!

Note: Use a good OEM regulator, e.g. the Paris-Phone/Valeo from Pelican.
- Loren

always use the same manufacturer for both the alt and the VR , as some alts like a slightly higher or lower charging current. Or you could get an adjustable voltage regulator and lower the "setpoint" to bring the charging voltage back down to 14.4.
- John Cramer

putting a resistor in parallel with the warning light bulb will put more current through the D+/61 "Blue Wire" circuit and provide you more excitation of the field at low revs.
- John Cramer


Power gets from the alternator to the fuse box via two paths. One is through the engine wire harness -- there are a couple of fat red wires and a brown ground wire in there.

The other path is through the heavy-gauge wire that runs from the alternator B+ terminal through that rubber grommet at the forward edge of the engine tin and to the lug terminal on the starter. Then it goes forward through the battery cable in the tunnel to the battery + terminal.

So that's six connections on the engine harness, one on the alternator, one on the starter and one on the battery. Also, hidden under the electrical console there's another 14-pin connector, you will want to make sure that's tight also. Then you have the fat red wires that come off the battery and go to the fuse panel, so there's a couple more.
- John Cramer

The 14-pin connector has particularly delicate silver-plated brass pins and sockets that you don't want to use anything more abrasive than a pink pencil eraser on ... chemical silver cleaner and pipe cleaners would be one way to clean them, but any way is going to be tedious! I recommend unbolting and removing the entire relay/fuse/CDI panel to have better access to the 14-pin connectors without placing undue stress on them.

After the 14 pins on the male side are clean ... I suggest spreading the pins VERY SLIGHTLY with the blade of an Exacto No. 11 knife.

The Blue D+ wire has to pass thru BOTH sets of 14-pin connectors.

- Warren Hall

First, the connector at the alt. must be soldered at the red wire and not crimped as was done by Porsche. Next, the same must be done at the starter connections.
Finally, the connections at the battery should also be soldered.
- Loren

current flows out of the battery through the ignition switch, through the bulb, into the blue wire, and into the alternator field, where it magnetizes the rotor. The rotor begins to turn, and this magnetic field induces a current in the stator windings which is rectified by the alternator diodes and fed back into the rotor by the voltage regulator. Once that happens, the potential difference between both sides of the warning light drops to zero and the light goes out.
- John Cramer

There are three wires connected to the Voltage regulator on the 'console,' or fuse/relay/regulator/CDI panel on the left side of the engine compartment. The brown wire -- 'D-', is ground, and the resistance measured from the regulator terminal to the frame of the alternator, and engine block, and any bare metal on the chassis should be less than 1 Ohm, always!!! A higher resistance than 1 Ohm is an indication of a high resistance/corroded connection somewhere in the wiring harness! The blue wire -- D+, is the exitation output from the alternator, and is connected to the warning lamp, and is used an input signal to the regulator ... it should always be higher than the battery Voltage, or the exitation diodes are bad inside the alternator. The black wire -- DF, is the output control signal from the regulator to the alternator, and should be a fluctuating DC Voltage that may show on the AC Voltage scale of a digital or analog multimeter as a 1-5 Volt signal ... if it is a steady DC Voltage, then the regulator is bad, or the brushes in the alternator are bad, or the field winding in the alternator is either open or shorted. If you want to determine which of those alternatives is most likely, turn the engine off, disconnect the black wire from the regulator, and measure the resistance from the black wire back to the alternator to a good ground connection, such as the brown wire at the regulator. If you can't get a good resistance reading, either the brushes are bad or the field winding is open. If you get a steady, non-zero resistance reading, the field winding and brushes are good, and the regulaor is bad!
- Warren Hall


While you've got the oil pressure gauge out of the dash, you might as well clean and tighten up the connections. They are, in order:

1. Red wire with black stripe, switched +12v that goes into one side of the warning lamp bulb holder. Clean the male terminals on the bulb holder with an ink eraser or mild abrasive like an emery cloth. Gently squeeze the brass "faston" connector with a pair of pliers if it's loose, but try not to damage the rubber insulation.

2. Blue wire that comes out of the warning light bulb holder.

3. On the "Console" in the engine compartment, the blue wire goes into the first 14-pin connector. From the first 14-pin, the wire runs to the regulator and then back to the 14-pin connector on the back of the console. Then it comes out again, as pin #11. I would use some contact cleaner and a piece of emery cloth to polish the pins, male and female, on that connector.

4. The last connection is where the blue wire joins the alternator, I think it's a small nut like a 5 or 6mm. Make sure this is clean and tight.

This should help. It's all there in the wiring diagram but there's a slight jump between the way the circuit is laid out and what's on the car, e.g. the 14-pin connectors are not shown as two parallel rows of seven, but rather a single row of 14 pins. . .
- Warren Hall

[kodioneill]

The best way to test a alternator is with a load tester and a volt meter combined. The alternator may put out the correct volts but the amps may not be there. Bad commutator brushes etc.. You should have the battery load tested also.

[E Sully]

You could try removing the 2 capacitors and wire directly to the regulator to make sure they have not failed and caused a problem, 2 blues to D+/61, black to DF.
The black wire you are unsure of should be to the relay for the WUR, #3 in the diagram. Unique to the 73.5 cis.

[rpc356]

RWebb, thanks for the info. After a quick reading I saw a few things I can check out.

[rpc356]

So, even though I see 15-16V at the battery with the VR jumpered out, it's still possible that the alternator is not producing enough amps? Just verifying, as this isn't my strong suit. I have a just-rebuild alternator that I can swap in. Seems like that may be a worthwhile effort.

Originally Posted by kodioneill

The alternator may put out the correct volts but the amps may not be there. Bad commutator brushes etc..

[rpc356]

Originally Posted by E Sully

You could try removing the 2 capacitors and wire directly to the regulator to make sure they have not failed and caused a problem, 2 blues to D+/61, black to DF.

Thanks Ed. I did remove the two capacitors, but no change.

Originally Posted by E Sully

The black wire you are unsure of should be to the relay for the WUR, #3 in the diagram. Unique to the 73.5 cis.

Doh! I should have remembered that, as I was just testing the WUR a couple months ago using that very diagram.

[clarkd]

It reads like you have full field tested your alt and have output, but don't have a reference voltage going to the VR. Does your alt have field diodes?

[rpc356]

Originally Posted by clarkd

It reads like you have full field tested your alt and have output, but don't have a reference voltage going to the VR. Does your alt have field diodes?

There are two sets of diodes, so I assume the answer is yes. Here's a description with the role of the diodes (thanks to 304065):

The alternator consists of two basic parts: the Rotor, which is the part that "rotates", connected to the car via the brushes, and the Stator, which is the part that remains "static," which is connected to two sets of output diodes. One set of output diodes goes to the B+ terminal-- it's function is to "rectify" the alternating current induced in the stator into an overlapping series of direct current pulses that charges the battery. The other set of output diodes (called the "trio" even though in motorola alternator's its a single diode) takes some of the alternator output and routes it to D+/61 (the "blue wire). This is used both to illuminate the warning lamp and also as a reference for the voltage regulator-- the voltage regulator compares the voltage coming off D+/61 to the "set-point" voltage and varies the DF voltage (DF is "dynamo field") that is flowing to the brushes and the rotor to achieve the set-point value.

How would I test this hypothesis? I have a just-rebuilt alternator that could be installed, if that helps.

[kodioneill]

Load test

[rpc356]

Originally Posted by kodioneill

Load test

I will pull the alternator and replace it with the rebuilt one, since the current installed alternator is suspect. Probably tomorrow. I'll report back what I find.

[rpc356]

Well, halleluiah! I swapped in the rebuilt alternator and am now seeing very healthy charging voltages. Thanks for everyone's comments, but particularly to kodioneill who had the key insight that the alternator could produce good voltage but fail to produce sufficient amperage. That's not a failure mode I saw in any of the threads I read.

Thanks again, folks!

[copbait73]

Assuming you still have two batteries, disconnect them and check each individually. In the good old days of everyday longhood driving this was usually the cause of many electrical issues.

[rpc356]

Originally Posted by copbait73

Assuming you still have two batteries, disconnect them and check each individually. In the good old days of everyday longhood driving this was usually the cause of many electrical issues.

I aspire to have two batteries some day, so will keep that in mind.

[clarkd]

What was the brand/model of alt you removed, and did you replace it with the same model? This information may be helpful to someone in the future.

[rpc356]

Originally Posted by clarkd

What was the brand/model of alt you removed, and did you replace it with the same model? This information may be helpful to someone in the future.

The one I removed was a SEV Marchal 712 237 02, according to the data plate. I replaced it with one that appeared identical, except that the D+/61 terminal was slightly shorter (not long enough for two nuts). The photo below is the one removed, minus the data plate.

[Herb_911_76]

I realize this is an old post but I have a similar charging problems and my 76 Euro targa has the exact same SEV Marchel alternator.

Current symptoms: low charging voltage: 12.2V at 3000rpm, 12.1V at idle, 11.8V with headlights on, although all slowly climbing (maybe one tenths every 5 minutes). 12.2V with engine off! Another (related?) symptom is occasional clicking of fuel pump relay and relay getting very hot (can’t touch after a while). Dash alt light works correctly: on with ignition on, off with engine running.

My story: misfire and stalling, low battery voltage led me to investigate alternator, removed and had it tested locally => “all is good”. Replaced Voltage regulator with solid state. In a state of denial, I went on to troubleshoot misfires by trouble shooting CIS (learned a lot), but now I am back to blaming the electrical system. I measured 26V AC across battery terminal => suspect diodes => removed alternator again, found diodes to be fine, but evidence that the six leads from the windings to the alternator overheated as insulation is brittle and copper strands seem oxidized => replaced insulation with heat shrink tubing = > reinstalled alternator=> same problem reading low DC and 26 VAC => now find that I also read AC with engine off celebrate invention of first AC battery, but quickly realize my cheapo Harbor Freight voltmeter is crap, a Fluke only reads a few mV AC, unfortunately also confirms low DC charging voltage.

My questions:
Could my fuel pump drag down the system voltage?
Is this a typical failure mode for this alternator?
What is the correct replacement part number (I tried replacing with new a couple of years ago but ended up with one that was too long).
Any other words of wisdom that can help me trouble shoot this?
Did I just answer my own question? (=>should I check current draw on the fuel pump?)