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Until a couple of weeks ago my 912ULS started easily regardless of the weather. Then it became hard to start and finally last Friday it wouldn't even fire. My son and I determined there was no spark at all. We checked the usual suspects; key switch, ignition switches, ground, etc. After thorough inspecting all the FWF wiring I started tracing the AC strobe circuit wiring from the regulator back to the strobe box. My logic, or maybe wishful thinking, being to eliminate the simple things before proceeding to resistance measurements. What I found was a crimp connector (blade type/quick disconnect) in one leg of the strobe circuit behind the sets that had obviously been hot enough to melt the plastic/nylon insulation and, as I could not pull it apart, maybe welded itself together? When I disconnected this circuit from the regulator the engine fired up normally. I have not reconnected the strobe and won't until I understand what has happened as I have a strong aversion to fire in the cockpit. An ohmmeter shown there are no shorts to ground in the circuit. The connector was well insulated and located such that a short is very unlikely. I didn't measure across the strobe input (Illusion Strobe Systems). Aside from determining the problem with the strobe I'd like to understand: a) why a short in the generator/lighting circuit would kill all ignition b) shouldn't this circuit be fused to prevent ignition loss c) if this problem had occurred in flight would it kill the ignition? Until I can resolve these questions I'm grounded. Thoughts?
thanks - Mike
  • Re: STROBE CIRCUIT OFF GENERATOR OUTPUT (912ULS)

    by » 9 years ago


    Hi Michael,

    Loose connectors can arc. Your wiring in your plane may have been installed in such a way that it grounded out everything when this shorted. This for us is an unknown. What type of plane? Factory or owner built? Could a wire have rubbed through the insulation some place? Strobe box miss mis-wired? Could wire size be too small? Just a few ideas to look at.

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


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