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Tach Leads on 912ULS

in General Tech Discussion 11 years ago
Guys,
I tried searching but cant find which tach lead is positive or negative coming from engine tach coil.
My wiring diagram for instrument needs the neg and positive from tach leads from engine. Does it matter since it is a coil trigger

Chuck

Flying Wild Texas

  • Re: Tach Leads on 912ULS

    by » 11 years ago

    Charles,

    I don't think it matters. (someone correct me if I'm wrong.) I've only hooked up two types, the EIS 4000 and an UMA. The wiring instructions with those two instruments are like the 912 diagrams in that they don't specify a plus or minus wire. They just say to connect the two wires from the trigger coil to the wires from the gauge. I just arbitrarily picked which gauge wire to go with which trigger wire and and it worked.

    Bill.
    Thank you said by: Charles Sharrar
      
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  • Re: Tach Leads on 912ULS

    by » 11 years ago

    You are correct; it is an AC signal so it does not matter.
    Rob
    Thank you said by: Charles Sharrar
      
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  • Re: Tach Leads on 912ULS

    by » 6 years ago

    Hello everyone, I have a question on the tach wires also. I'm trying to hook up a VDO tachometer. My lead wires are different colors than described by the manual. Mine are red/white and green / white. Which is positive and do I ground one? The DIP switch has been verified but have seen different posts on the setting as well. Mine engine is new but an older model 912 UL any guidance would sure be appreciated.
    Thanks, Todd
    Thank you said by: COLIN JOHN WOOLLARD
      
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  • Re: Tach Leads on 912ULS

    by » 6 years ago

    I've got an issue with my tach on a Rans S-12S airplane, flying a Rotax 912 Uls engine. Just got done doing the 5 year rubber replacement, put everything back together and started it up. Got carbs tuned and took it out to taxi. Noticed tach would read normal, then the needle would start swinging back and forth; up to max, back to 0, then back to normal. Stayed there for awhile, then would start again. It's a VDO tach. Any ideas or suggestions?
      
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  • Re: Tach Leads on 912ULS

    by » 6 years ago

    Since you had your hands up on the engine working the best bet is you loosened a wire. Go to that black insulated wire up on the back of the engine that has two wires inside and follow it to the connector. Many are in the engine compartment. I think you may find your smoking gun there.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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