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Thread: 123 ig running tach wire question

  1. #1
    Member
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    Aug 2021
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    Surrey B.C.
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    123 ig running tach wire question

    Hello,
    I am installing a 123 dist into my 69t, when I removed the wires at the coil I noted the tach wire was connected to the 15 terminal of the coil. The car had a Mark Ten CDI ignition box which I have removed. Which terminal do I install the tach wire or do I need an adapter box for the tach to work?

    Thanks you
    Jake
    mbr#4161
    69 911t
    72 2002tii

  2. #2
    Probably best to ask the 123 vendor, they will know for sure and should be providing customer support I would think.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  3. #3
    Senior Member
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    Aug 2020
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    With no CDI system, the 12 volt wire from your ignition goes to the + ( also the “15”)
    coil terminal. The tach wire and wire to the distributor go to the minus coil terminal. As Ed said, if you have non-standard parts, the the vendor is the go to source. Do you have the original Marelli distributor?
    My 69T has a 4th wire that goes to the 15 terminal on the coil and it is used for a relay to park the rear window wiper.
    Steve

  4. #4
    Member
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    Aug 2021
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    Surrey B.C.
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    Ed, Steve thanks for your reply. When I spoke with the 123 vendor he said just hook it up as a regular points ignition. The reason I'm asking is with the tune box someone put in. Normally the tach is connected to the point side of the coil.

    The history shows that Grady Clay did some mods to the engine but no info on the Mark Ten box. When googled I didn't have much luck.

    I have a Bosch 001 dist that I have been running till now, when tested on the dist machine all was within spec. I'm having some mild popping coming out of the exhaust when cruise and decel. Check for intake and exhaust leaks, none that I found, and when I check my CO readings at the tail pipe a bit rich but the HC were well within reason. Thinking maybe the Box is causing it or points float.

    I have the 123 in our 2002 that is heavily modified and its been good for the car.

    Thanks
    Jake
    mbr#4161
    69 911t
    72 2002tii

  5. #5
    I wouldn't think point float at mild cruise RPM. Are the points the correct spring tension for a 911 as opposed to weaker spring points. Is the breaker cam lubricated? What is the air /fuel ratio at the RPM in question? A Delta MK 10 was a common upgrade, some references to it in "Up-Fixin" at the time.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  6. #6
    Senior Member
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    When I put in an MSD, the tach would not work, so needed a adapter from MSD. I think the non-CDI systems work with the tach because the dwell of the points is long enough for the tach to sense it. The CDI electronic systems go to fast, so the tach never sees any counts, so never moves. In the MSD, the adapter connects directly to the tach wire, so no coil connection is needed. If I misunderstand how these "older" tachs work, please someone correct me!
    Steve

  7. #7
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    thank you gentlemen.
    mbr#4161
    69 911t
    72 2002tii

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