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Thread: Key in Accessory position: messing up the points or rotor?

  1. #1
    Senior Member Veronica87911's Avatar
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    Question Key in Accessory position: messing up the points or rotor?

    I had some work on my fogs done on the 72 last week and the mechanic left the key in the accessory position for a minute or so to check the lights, voltage, resistance, etc.
    Since then, the car has been running rough, stumbling, low revs at times. Did leaving the key on without starting it do something to the points or distributor rotor?
    I remember when I first got the car, Kevin, my guy in Florida, mentioned never to do that, but I don't remember why.

    Any help is, as usual, much appreciated.
    Serge

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  2. #2
    member #1515
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    As long as it is in the accessory first position, no problem. If the fuel pumps are running and the CDI unit is humming, you have the possibility of burning the points. That is in any car with points.
    Although I think with CDI you have less current running through the points than a normal Kettering ignition.
    David

    '73 S Targa #0830 2.7 MFI rebuilt to RS specs

  3. #3
    #2264 classic's Avatar
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    +1 with CDI very little amperage through the points.

    Kettering..... You can weld the points
    Tony

  4. #4
    CDI trigger circuit has a 33 ohm pullup resistor so +12.6v/33 ohm = 380mA of current when points are closed. This is barely enough to keep them clean.

    Kettering = 4 amps (+12.6v/2.1 ohm coil primary resistance + 0.9 ohm ballast resistor (in run position) = 4.2 amps or 53 watts (53 joule/sec)

    So don't leave your 911T to idle in the Vermont winter -- when it stalls it will burn the ignition up (old Up-Fixen article!)
    1966 911 #304065 Irischgruen

  5. #5
    Senior Member
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    I agree it won't cause harm, having just performed the "key test for dummies" last week. I left the key in the accessory position to turn the wheel while I pushed the car around the garage. Forgot about it and left it that way for 2 days. No problems; not even battery drain issues.
    Jeff Jensen

  6. #6
    In the Accessory position, only minimal accessory circuits are activated - nothing related to engine operation. Therefore, should be fine. If otherwise, the wiring has been modified.

    Sherwood

  7. #7
    Senior Member Bob Harriman's Avatar
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    This may not exactly apply to the original question since my key was in the ON position not the acc position but while doing electrical work on my 69 for a couple of hours with the ignition on my coil started leaking and was ruined.

  8. #8
    Bob, makes sense, 912 never had CDI.
    1966 911 #304065 Irischgruen

  9. #9
    Senior Member Bob Harriman's Avatar
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    I figured it wouldn't apply

  10. #10
    With an induction ignition system, when the ign. switch is ON and the points closed, there's a direct current path from battery > ign. sw. > coil > points > ground. The coil is basically an electromagnet designed for intermittent operation (on-off-on-off, etc.). With constant current flow, It can overheat, expand, then leak. The points in a CDI system are subject to much less current.

    Bob, A 6-cylinder engine will make you happier.

    Sherwood

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