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Thread: Bosch CDI in '68 911- Alternator light problem?

  1. #1
    Senior Member 72tii's Avatar
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    Bosch CDI in '68 911- Alternator light problem?

    I just finished installing a Bosch CDI, coil and tachometer transmitter tonight. It started up on the first try and pulls much stronger with a smoother idle.

    However, I noticed that the alternator light has changed from a very faint glow before to a more pronounced glow with the headlights on. When using the turn signals it pulsates a little brighter with each click. This is not noticeable with the headlights off, probably because of the sunlight I'm guessing.

    When I had first installed the H4 headlight assemblies, the glowing was similar to tonight, but it was greatly reduced after installing headlight relays (plus the instrument lights were much brighter).

    I hooked the wiring up as follows:

    CDI- pin A to coil 15 terminal, pin B to keyed power, pin C to black Pertronix wire and pin D to ground on the side panel.

    Tachometer transmitter- pin A to ground on the side panel, pin B to coil 15 terminal and pin C to tachometer wire.

    The red Pertronix wire is attached to keyed power along with the fuel pump.

    I've got the single red keyed power feed wire in the engine compartment running the Pertronix, CDI and fuel pump with a four-way connector. Do you think this is pulling too many amps now and causing the alternator light to glow brighter?

    Thanks in advance,

    Mike
    1968 911 #11830241
    Early S Registry #810
    R Gruppe #461

  2. #2
    Hi Mike.

    Congratulations, your CDI wiring and tach transmitter are correct.

    The CDI pulls a few amps, not as much as an MSD but still probably five amps. However, in my '66 with the identical setup I have the CDI running off one pin of a wye connector, the other pin to the fuel pump, and the supply from the ignition switch. So I don't believe that in the absence of a short circuit, which you would notice by the smoke and flames coming from the engine compartment, that your problem is there.

    Since you figured out how to wire the CDI and transmitter you're obviously electrical savvy so fixing it will be easy. As you know, the warning lamp glows when battery voltage is higher than the voltage coming off the alternator. That is certainly the case when you turn the key on and the alternator's not spinning. If the light is glowing when the engine is running, that means one of a few possibilities:

    1. Failed output diode. This will show up as a ripple in the alternator output, if you have access to a scope. If you don't, a simple voltmeter applied to the battery terminals with the engine running will tell you whether the voltage is 14v, where it should be, or 12.6, the battery voltage. OK, the old Bosch voltage regulators have a set point of like 13.6v, which as the car ages and the connections oxidize is barely enough to charge the battery, but you get the idea.

    2. Bad voltage regulator. If yours is original it's a mechanical type. The modern ones, which have a virtually identical can, are solid state and do a much better job of regulating output voltage. In the threads below you can see I use a Transpo adjustable regulator, I have an original for concours.

    3. *** Most Likely Possibility* * * when you were mounting the CDI you jarred the connectors for the voltage regulator. If you got it from a later car, there's a possibility that it came with an in-line radio noise supressor. If one of these is installed between the VR wire harness and the VR, give it the water test by throwing it into the nearest convenient lake or stream. If it floats, retreive and reinstall.

    Seriously, go back and check the three-pin connector, these are very old and crumbly often, and the contacts within are oxidided. Any high resistance between the DF wire (black) and the VR or the D+/61 wire (small red, blue in the later cars) can give you that problem. The D+/61 in particular has a male-to-female faston quick disconnect that's covered in a molded rubber sleeve, pull this apart (carefully!) and clean the contacts, both sides, with an ink eraser, a very mild abrasive, some electrical contact cleaner or 9% pickling vinegar until the terminals are BRIGHT metal. Ditto for the contacts inside the three-pin plug and for the male pins on the voltage regulator.

    4. Alternator belt slipping. Tighten per factory manual.

    There could be other issues, but have a go at checking for oxidiation on the contacts and report back.

    The CDI really makes a difference, right? My car HOWLS since I did that mod.

    For more info about the SWB electrical systems, I have been collecting it here:

    http://forums.pelicanparts.com/showt...0&pagenumber=1

    http://forums.pelicanparts.com/showt...t&pagenumber=1

    Good luck!
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    1966 911 #304065 Irischgruen

  3. #3
    Senior Member 72tii's Avatar
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    Thanks, John for the detailed reply!

    I did have the voltage regulator disconnected when I was installing the CD as I needed to drill a couple of holes in the side panel to make everything fit and removed it from the car to do this.

    I cleaned all the connections to the regulator, but am still having the problem. I checked the voltage at the battery before and after cleaning and am getting 13.2 with the headlights off at idle and 12.8 at idle with the headlights on. If I rev the engine up to around 1500 rpm, it increases to around 13.1 volts. There was no change after the cleaning. I did have the original regulator on the car yesterday and installed a new, solid state one today with no change.

    Both of the regulators are Bosch, but I don't know what brand of alternator is on the car as I bought the engine used. If it's a different brand alternator, is it possible that the Bosch regulator is not compatible?

    I guess I need to remove the alternator tomorrow and check/clean the connections on the back. Does it sound to you like I need to install a rebuilt alternator? I think it's odd that this just started with the CD installation, but I know it's possible anything can happen with electrical components.

    Let me know what you think and thanks again.

    Mike
    1968 911 #11830241
    Early S Registry #810
    R Gruppe #461

  4. #4
    Mike, you are on the right track with your diagnosis.

    13.1v at 1500 rpm at least tells you that the alternator is showing up for work. I would be more concerned if the voltage were the same as static battery voltage.

    You have probably seen a sticker that says "Generator und regler mussen vom gleichen Hersteller sein" or something like that. (I think the old ones say "lichtmaschine" which is a cool word) but anyway what they are trying to tell you is that the alternator and voltage regulator must be from the same manufacturer. The REASON for that, other than it being an unlawful tying arrangement in violation of the Clayton Act, is that the regulator senses the voltage coming in through the D+/61 circuit which comes off the diode trio (or in older alternators like ours, a single isolation diode) and then alters the Dynamo Field voltage (in the DF wire, funny how they have the same initials) in order to make the output voltage equal the correct value. This output voltage is the "set-point" and if you have an adjustable voltage regulator you turn the little potentiometer until that voltage is achieved. The trouble arises if you use a Bosch VR with a Marchal alternator-- the construction of the alternator requires a specific DF voltage to achieve the desired output voltage, but a VR from a different manufacturer outputs a different DF voltage, which throws everything off.

    Anyway, I would check the contacts on the alternator, with the change in weather there may have been some oxidation. That' 99% your problem, unless you see an alternator that says "SEV MARCHAL" on the back. . .
    1966 911 #304065 Irischgruen

  5. #5
    Senior Member 72tii's Avatar
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    Smile Charging problem solved

    You were right on the money, John. I pulled the alternator to clean the contacts and found a Motorola unit. After cleaning the contacts, I was getting the exact same readings at the battery.

    I went down to Zim's Autotechnik this morning and bought an adjustable voltage regulator, adjusted it to 13.8 volts and buttoned it up.

    After pulling the alternator, I had read several posts on Pelican regarding verifying your alternator manufacturer without removal. The Motorola/Marchal alternators have a 16mm shaft and the Bosch units have a 14mm. No big deal for me as I wanted to make sure the contacts were clean anyway.

    Anyone want to buy a barely used Bosch electronic voltage regulator?

    Even though the alternator is now charging correctly, I am still getting the alternator light glowing faintly when I step on the brakes and/or use the turn signals. I have changed out the bulb holder for the alternator light and installed a new bulb, cleaned the fuse contacts and secured the wiring at the fuse block. Where should I look next? Could it just be resistance in an old ignition switch causing this?

    Thanks again,

    Mike
    1968 911 #11830241
    Early S Registry #810
    R Gruppe #461

  6. #6
    One problem solved, another one pops up!

    OK, so you have a steady 13.8v coming out of the alternator, good job.

    Let me think about it. . .

    FRONT

    4W marker
    21W signal

    REAR

    21W signal
    21W reverse lamp
    4W marker/21W stop

    Ok, and there are two of those per side. Which means that when you hit the brakes, the load should be 21W x 2 = 42W / 13.8 v = 3.04 amps. Ditto with the turn signals, 4x21w = 84w/13.8v=6.08 amps. Plug those values into Ohm's law and you get 13.8 = 3.04 x 4.6 ohms and 13.8 = 6.08 x 2.26 ohms.

    Now, I would be willing to bet a large Warsteiner that your bulb circuits are showing WAY more than 5 and 3 ohms. Have you had the bulb holders out lately? They come out with a philips screwdriver. Once you have one out, you should see the bulb holders with wires going to the back, and if they are anything like mine, you will see about four decades of greenish-brown oxidation and crud on the connectors. The wires will probably be so weak and work-hardened where they join the flag-style faston connectors that any flexing will break them. Also, you may see cuts in the wire which have exposed the copper to air. All of this can be cleaned up with clear heat-shrink tubing and the correct flag-style connectors from www.eagleday.com. If you have to replace wires, it's a very good idea to use the same color conductor as original, this makes diagnosis easier (and keeps the Porsche G_ds from getting angry besides).

    You wouldn't believe the crap I found behind mine when I did this. I carefully removed and restored the wires, which were covered in overspray from three paint jobs over the years, cleaned the faston terminals on the bulb holder with an ink eraser and electrical contact cleaner until they were nice and bright, replaced the GROUND WIRE which was the source of most problems, and replaced all the bulbs. Also, some PO idiot had switched the signal and marker wires, so for about a decade when he went to signal a turn he did so with the wimpy little 4W marker lamp, I'm suprised he didn't total the car.

    Anyway, your problem is due to high-resistance connections in the bulb circuit somewhere. It makes sense to start with the bulb holders, because they are just about the worst spot, exposed to air and water and can't dry out on their own. Once you get them cleaned up, the resistance will go back down, and you shouldn't get the huge voltage drop that's causing the alternator light to backfeed from the battery. The longer the problem continues the worse it actually gets, because the higher the resistance grows, the hotter the circuit gets, increasing the likelihood that a wire will melt and touch another one or the ground and then it's show time.

    Good luck!
    1966 911 #304065 Irischgruen

  7. #7
    Senior Member 72tii's Avatar
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    Update on voltage readings

    Thanks for the post, John. There's a new twist today.

    I have been out in the garage this morning checking the voltage again and have found something interesting. The voltage at the regulator with the blue wire is reading 14.6 volts while I am getting the 13.8 at the battery that I set yesterday. I checked all the ground points on the car and didn't get any unusual readings on the meter with it hooked directly to battery ground. It appears that I am having to up the output at the regulator to get 13.8 at the battery. I am going out next to check the voltage at the starter and see what it reads.

    I'll check all the bulb holders and grounds in the lights and report back after I get this voltage drop figured out.

    Mike
    1968 911 #11830241
    Early S Registry #810
    R Gruppe #461

  8. #8
    Senior Member 72tii's Avatar
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    Update, part 2

    I cleaned the connections at the starter and got exactly the same as the battery with the engine running- 13.85 volts.

    Then I removed the alternator and cleaned the ground strap on the case and this made an improvement. It's now 14.1 at the regulator, but the light is still dimly glowing.

    After cleaning all of the contacts on the lights front and rear, I still have the same problem with the alternator light pulsing to the turn signals and brake lights.

    I'm thinking about just installing a 91 ohm 5 watt resistor on the light as per the factory technical service bulletin on upgrading to an internally regulated alternator as a last resort.

    Thanks,

    Mike
    1968 911 #11830241
    Early S Registry #810
    R Gruppe #461

  9. #9
    Mike,

    As you saw when you cleaned the ground to the case, removing the oxidation makes a big difference.

    The "blue wire" is only useful from zero to about 1200 rpm. It's job is to provide "pre-excitation" current to the alternator rotor, magnetizing it, so that a current can be induced in the stator, rectified by the diodes, and fed back to the rotor through the DF wire. But this "boostrapping" cannot occur without some initial excitation voltage. So when you turn the key on, power flows out of the battery, through the ignition switch, into the bulb holder for the warning lamp, through the filament (lighting it) and then back through the blue wire, into the voltage regulator, which sends it into the rotor and then to ground.

    The reason I mention the current path is that a high resistance in that circuit serves to RAISE the alternator's "zero-ampere RPM" or the point above which it begins to produce current that is fed back through the blue wire against the current flow from the battery. When the current from the alternator matches that from the battery, the electrical pressure (voltage) is the same on both sides and no current can flow: the bulb goes out.

    Adding the resistor in parallel (anywhere from 68 to 91 ohms is a range that has been used in the past) merely lowers the resistance in the blue wire circuit. The 1982 and later cars used an internally regulated alternator with a 4w bulb. When you convert an earlier car, the diameter of the bulb holder isn't big enough to accomodate a 4W bulb, so you use the old 2W with a parallel resistor to get enough current to drive the internal regulator.

    Well, to be fair the other purpose the blue wire serves is to feed back the charging voltage to the VR so it can set the DF output, but since you are already getting the voltage you want, that's not the issue.

    As you can see from the explanation, that's a solution to a different problem, one that would be solvable in any case by cleaning the oxidation from the blue wire terminals. One particular trouble spot in the SWB cars is the faston connector for the blue wire to the voltage regulator-- it's an inline 1/4" male and female protected by a molded rubber boot, it gets hot and gets dirty.

    You are correct to focus on the bulb sockets. There's one more place you should try to find the high resistance, a known culprit that will result in your lying upside down with your head next to the pedals, are you ready?

    The 1968-vintage Stribel flasher, it looks like an aluminum can, underneath the drivers floorboard. The turn signals run through it. Try cleaning the contacts carefully and check the wires for anything unusual. Also, because your car is a 1968, the first year of the DOT-mandated dual circuit master cylinder, you should have a brake light switch installed with two screws on the pedal cluster. Carefully remove it and note its orientation for reinstallation, it works opposite to the way you would think.

    I reverse-engineered the flasher unit, here is how it works if it turns out to be the problem.

    http://forums.pelicanparts.com/showt...hlight=stribel

    Good luck! You may want to dial the battery voltage back to 14.0. What kind of batteries do you have? If they are lead-acid interstates, make sure the voltage is in the high 13's, don't want to boil the acid. An Optima or Odyssey can take higher voltage but you might see fluctuation in the tachometer if it gets too high.
    1966 911 #304065 Irischgruen

  10. #10
    Senior Member 72tii's Avatar
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    More contact cleaning

    Hi John,

    After turning the adjustable regulator back to 14 volts, I am now getting 13.2 at the battery. The battery I am using is a Miata AGM that is only four months old. Even though there is a difference in the charging voltage, I haven't had a problem with the battery losing a charge yet. It starts up fine every time.

    I cleaned all the contacts at the hazard flasher unit and the brake pedal switch with no change in the alternator light. I even ran a wire from the connector coming off the voltage regulator to the alternator light with the same results as before.

    Since all of the grounds on the car test good, doesn't it seem that there might be a problem with the alternator because of the difference in the voltage at the regulator as opposed to the other points on the car? I'm thinking of taking the alternator down to have it checked out. I suppose if the alternator checks out all right, it might be a problem with the alternator harness going to the battery and/or voltage regulator.

    I only have one keyed power wire in the engine compartment and it's running the fuel pump, CDI box, Pertronix and tachometer transmitter. Do you see any problems here?

    Thanks again for your responses. Looking forward to hearing your thoughts on the latest.

    Best regards,

    Mike
    1968 911 #11830241
    Early S Registry #810
    R Gruppe #461

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