Alternator Issues

[santee]

Greetings all! This one is long but not complicated.
This is a '74 911 that is having alternator problems, it is not charging, lamp stays light all the time when key is off and 0 to 2000 RPMs. (Can not go over 2000 RPMS, new engine) The alternator is a new style Bosch alternator with an internal regulator. (Black wire was removed from wiring harness)

Here is what I have done and my results:

1) I disconnected the lead going to the fuel pump ('74s run all the time when the key is on) When I first turned the key over with the alternator out, the alternator lamp stayed on and I noticed a high pitched noise coming from the back of the engine. It finally stopped after about 15 seconds and the alternator light went out. ( I thought the light should never come on if it is not grounding through the alternator)

2) I checked the voltage on the blue wire (D+/61 terminal) coming from the lamp. It registered 10.2 volts.

3) I grounded the blue wire. The lamp came on but several components on the side of the firewall clicked or buzzed. I am attaching a photo of the components.

4) I pulled the small round black relay (WUR relay) and the lamp still lights and the clicking stopped. But there is still a slight buzz.

5) I pulled the blue lead going to the metal rectangular component (old external regulator) and grounded the blue wire. The light comes on and there is no buzz or clicking.

I checked behind the lamp on the dash and there is no resistor installed. (Referring to Pelican posting for upgraded alternators)

I guess my question is... Is it normal for these components to click and buzz when you ground out the blue lead to the alternator? From what I can tell, the blue wire is a straight wire to the alternator that only passes through the connector on the firewall.

This is an updated post, Jim and John helped make the issue much clearer and I am truely grateful.

I will make sure the old external regulator stays disconnected, however I am still puzzled why they are affected by the grounding of the blue wire (D+/61 terminal) coming from the lamp.

I will continue to troubleshoot....

Any suggestions would be VERY helpful!

Thanks,

Stephen

[Jim Sims]

I would recommend you cease the random grounding before you burn out something like an alternator diode or the CDI box. Get a schematic and understand the system first. Jim

[santee]

Jim- The blue wire going to the alternator charges the field. It grounds out when the alternator is not running and the alternator light comes on. When the alternator is actually charging, the ground goes away and the light goes off. Its a simple system. Random grounding?

[Jim Sims]

On a 1974 there are 3 blue wires in the area you are working with; one leads to the WUR relay the (round black relay you unplugged) and the others attach to the "buzzing" box you circled which is an external voltage regulator which should have been removed or at least disconnected if an internally regulated alternator is being used. Also the black wire in the harness at rear of alternator should be taped off and not connected to alternator. The WUR relay clicking is probably due to it switching when you ground a blue wire. On 1973.5 and 1974 CIS systems the fuel pump runs whenever the key is on even if the engine isn't running as these years do not have an air flow switch. If the alternator light remains on after addressing the external relay issues as stated above you may need to put a resistor in parallel with the generator light. If the problem persists after that, you may have too much voltage drop between the alternator and the forward part of the car (bad connection?) or a bad diode in the alternator. Cheers, Jim

[304065]

Stephen,

First, as a new poster you may want to avail yourself of the wealth of information contained in the archives here. Use the "search" feature and look for posts by early_s_man or lorenfb, both have many many years of electrical diagnosis experience.

Now, there's no substitute for having the correct wiring diagram, so get one, even if you have to buy the factory manual. If you look on the pelican main page, there's a link to electrical diagrams: '74 isn't covered but you can get some sense from the 73 with CIS addition.

You are correct to focus on the blue wire in the charging circuit. Simply put, current flows from the battery, through the ignition switch, then into the bulb holder for the warning lamp in the oil pressure gauge. From the other terminal of the bulb holder, current flows through the "blue wire" back to the electrical console, where it connects to the voltage regulator, and then goes to pin #11 of the 14-pin connector. The engine wire harness connects to that 14-pin connector, and the blue wire continues within that harness, connecting to the D+/61 terminal on the alternator.

Operation is as you have described: with the ignition on and the alternator not turning, current flows through the blue wire into the rotor and to ground, energizing the rotor. Once the car is started and the rotor moves, the energized rotor induces a current in the stator which is rectified by the "trio" diodes (some early cars had only one) and fed back into the blue wire circuit, causing the potential difference to balance on either side of the bulb filament, extinguishing the light. If the light's still glowing, that means that you have more voltage on the battery side than the alternator, indicating a charging problem.

Disconnect that external voltage regulator. That's the problem.

The relay has NOTHING to do with the charging circuit, if it's buzzing, that's a separate issue unrelated to the alternator.

Good luck!

[santee]

Thanks for the advice. This has been my first post but I have been searching Pelican and Rennlist for about 4 months now. This has been the only issue that previous searches have not helped with. So I am in awe at the knowledge that is on this site!!! I have read many threads that deal with the alternator issues but of course, each are slightly different.

I'm going to clean up the original post to keep the issue clear.

I do not think I was clear last night... I was frustrated.

I have a Chilton's wiring diagram; it seems to be accurate, just difficult to read.

The car has the newer style alternator with four wires. A brown wire that is clearly grounded to the engine, another brown wire (ground) coming from the wiring harness, a blue wire that goes to the alt lamp, and the twin red wire that leads to the starter. The black wire has been removed, probably by PO when they upgraded to the alternator with the built in regulator.

On previous searches, I came across the specs for the resistor that goes behind the lamp, 61-91 ohms, 5 watt, when doing the conversion. I plan on getting that installed. The Pelican bulletin lists a connector, is that to make the resistor install easier?

Should I be getting the same voltage over the blue wire (D+/61 terminal) as I get when taking a reading from the battery? IE, I get a 12 volt reading at the battery but only a 10.2 volt reading when checking the wire.

I still have the alternator out, I may take it to another shop and make sure that it is good... but I John I agree with you, I think there are other issues with the electrical. Do you or anyone else know if this car came with a factory alarm as an option? There was an old alarm on it. I took it off. Many of the wires were cut. I alarm was patched in to the fuel pump circuit and that was fun tracing down.

Also, that’s for the clarification on the fuel pump. I was never sure if it should run all the time. I did have other 74 owners tell me that theirs did too, so I figured it was normal.

Thanks,

Stephen

[Early_S_Man]

Stephen,

Below is a '73 wiring diagram, which, for your purposes ... is identical to the '74 electrical system for the alternator, regulator, CDI, etc.

The regulator shown is for a Motorola/Marchal/SEV alternator. Your alternator should have M16 x 1.00 threads on the shaft.

The Blue #61 wire should never be grounded during testing! It supplies pre-excitation current below the Zero-Ampere cutoff speed (rpms) ... and has your alternator warning lamp filament bulb in series with battery from the ignition switch. The buzzing you hear from the regulator is the relay attempting to apply excitation current to the field winding in the alternator rotor ... but you have grounded the path via the Blue wire, and all attempts to increase Voltage output are failing due to the presence of that grounded Blue wire!!!

[santee]

Well, that explains it! I wish I still lived in Abilene I'd buy you a beer!

Okay, no more "Cowboy Diagnostics", I'll get the alternator checked again, clean all connections, solder them if needed, clean all grounds, and install the resistor on the lamp. Then go from there. Do you know if the rebuilt Bosch (AL400X) alternators with the Valeo internal regulator are any good? That is what I presently have.

Thanks again!!

Stephen

[Early_S_Man]

A few discrepancies noted ...

1. That is not a '74 regulator on that panel, it is '68 - '73!

2. I assumed you meant a four-wire '75 - '81 980 Watt Marchal/Motorola/SEV alternator that still used an external regulator was present. A pic of the backside of the alternator would clarify which alternator you have ...

3. The old regulator should NOT still be hooked up to the wiring harness if the alternator is the IR-type! Internal regulator alternators were mfr Valeo or Paris-Rhone.

I am not familiar with Bosch alternator with modification to install internal regulator ...

[Jim Sims]

The clips (Porsche calls them "cable dividers") to mount the resistor in parallel with the alternator light are part number 111971511; Pelican has them for $1.00 each. They are handy to use as they allow one to bench solder the resistor and then plug in the assembly without having to solder in place near the dash behind the gage. The 911 Haynes repair manual contains a complete 1974 wiring digram and key; it's not in color but is quite usable as the wires are labeled with their colors. Our host Pelican sells this Haynes manual for a reasonable cost or one can often find them used for even less. One more caution with grounding wires in a 911; there are numerous circuits that are unfused and grounding a hot wire can lead to melted wires in the harness. I have the 1974 to 1977 911 factory illustrated parts catalogs if you need a part number. Cheers, Jim

[santee]

This is about a good of pic I can give you right now. It shows the back side of the alternator. The black regulator says Valeo made in France. There are three terminals on the backside.

-Stephen

[santee]

Normally I don't ground items out, but I've done this as a quick test on American vehicles... (enough said right? )

I actually do have the Haynes (not Chilton), 101 projects for 911 & engine, and Haynes restoration of the 911. What gets me in trouble is not knowing the modifications done by the PO. And after all, I found this car in '99 in a field near a driving range for sale... Auction car. It was cheap and needing help.

[304065]

Well that's definitely an internally regulated alternator. Much simpler to wire than the external reg'd version. Remove that external reg.

[santee]

$1.00 for resistor
$ .50 for two connectors
$7.99 for Di-electric grease

Great advice from this forum... priceless!!

It's up and charging now. It runs soooo much better to. I soldered all the connections that were crimped for the alternator, cleaned them, took off the fresh paint where they grounded, installed the resistor, and used the di-electric grease.

Thanks again!

I'll post pics once it is finished.



-Stephen

[Early_S_Man]

Glad it is working, now!

Just for the benefit of searching Pelicans ... here is the updated alternator bulletin:

[surgerypending]

Anyone know where I can find one of these resistors for my dash light?

[cmonref]

I got one from an electronics supply house. Radio Shack does not carry them.