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Thread: Alternator Question

  1. #1

    Alternator Question

    Hello all - have a 69 911T with MSD ignition, but all else stock. I've had a few instances where my tach has bounced around randomly cruising, then acted normally. Last Saturday, I was driving, had to honk the horn and got no response. Later in the drive, the car died and wouldn't turn back on - no response from turning the key. I was also low on gas, but the light was not on consistently, so I'm not sure that was the main problem, but when I added a couple gallons, it started up and was able to drive a couple miles home. I bought a voltmeter and put it in the cigarette outlet - generally speaking it was reading anywhere between 12.75 to 13.5 under normal load/idle and up to 14 under full throttle.

    Would any of this indicate that my alternator is going or does the volt readings seem normal and perhaps it was a gas issue and my dummy light just wasn't reading all that well?

    Thanks in advance - Tim

  2. #2
    Senior Member
    Join Date
    Aug 2020
    Location
    Shawnee, OK
    Posts
    179
    Also have a red 69T with MSD. My tach would not read anything until I got an adapter from MSD then no problems. To me sounds like you have a battery problem. Check the battery voltage without the car running. It should be 12.6 volts if the battery if fully charged. about 12.0 if the battery is about "empty". Then check the battery voltage with the engine running. It should be in the 14 volt range. If these check OK, then we would have to look elsewhere. If the starter would not spin when the engine is off, not a lot of choices for the problem-ignition switch, starter relay, starter, -but since your problem is intermittent, I would guess the ignition switch-my starter was intermittent and the ignition switch was gradually coming apart. Was able to remove, disassemble, re assemble and no other issues. Good luck!

  3. #3
    Senior Member Scott A's Avatar
    Join Date
    May 2014
    Location
    South East USA
    Posts
    897
    If i added my opinions,
    your voltage going from 12+ to 14 sounds good.
    if you car was hot...sometimes starters don't turn when hot(and will do 'nothing')...(sometimes you can take them apart, clean, especially solenoid area and that might solve that)
    if the starter does 'nothing', then get someone holding the key to 'on', then simultaneously tap the starter body with a big screwdriver or crowbar...or a pipe, if it springs to life, then there is your problem.
    the first thing i would do is clean your connectors at batteries, starter, and if you can reach them, behind the key. (and every body ground you can find)

    Current long term ownership: 63 Cab, 71 911, 74 914

  4. #4
    Thanks, guys. Will troubleshoot those areas you both mentioned.

    Tim

  5. #5
    Senior Member
    Join Date
    Dec 2008
    Location
    Black Mountain, NC
    Posts
    539
    "IF" you decide to use a tac adaptor dont get the klunky MSD unit Get a "TacAdapt" from Bob Ashlock on the forum here. much nicer and small easy to hide and hook up.
    On the MSD I am running one in my 66 912, on setting it up MSD said with Bosch system you do NOT need the tac adaptor, well not correct. So after making a nice aluminum bracket for the MSD unit to bolt into where the 911 oil tank mounts, nice & out of the way. they then tell me i should try the adaptor to see if the tac will work again.
    You would think they would know their product better.

    Regards

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