I recently had my RV12iS (iS engine, dual G3X, TT 104 hours) painted. On my initial preflight and engine run up for my trip home from the paint shop the Lane A and B switches and associated lights functioned normally. The flight was uneventful, and the engine appeared to be running reasonably smoothly, with minimal vibration. However, on my next preflight I noticed the Lane A light never illuminated, regardless of Lane A and B switch positions. The function of the Lane A switch itself appeared normal, with expected drop out of engine instruments, and normal running of the engine when Lane B was turned off. Lane B switch and light behaved normally with expected drop out of engine instruments.  

ECU faults were noted in the Engine Information page only when either switch was off, but with both on, no faults were noted. I concluded the problem was with the indicator light.

Investigation included:

  • Removal and inspection of the ignition switch module.
  • Inspection of the wire harness d-sub pins at both ends of the cable connecting the ignition module to the HIC connector module. Special attention was given to the wires associated with the indicator light per the schematic diagram.
  • Wiggling all connectors on the HIC module to see if the Lane A light would briefly come on.

No abnormalities were found up to this point.

I next pulled the cowl cover and inspected the Rotax engine fusebox. While I could not find documentation as to specifically how the indicator light is wired through the fuse box (or what each fuse in the fusebox is for), I did notice a 2 AMP fuse was blown. I replaced the fuse, and the Lane A indicator light now functions normally. I have cycled the avionics on and off, as well as started the engine numerous times since, and Lane A light continues to function normally. With both Lane A and B switches “on”, there are no ECU faults.  

I also performed a dynamic prop balance post painting, Prior to painting the IPS was 0.04. Post painting it was 0.14 with improvement to 0.02 IPS post balancing. The minimal vibration I noticed previously is improved post balancing.

My questions:

  • Although the light and Lane switches appear to be working normally now, should I be looking elsewhere for a cause of the blown fuse?
  • It seems coincidental that the problem occurred after painting. Could this be vibration related?
  • Can anyone point me to a description of what circuit each fuse in the fusebox protects?

Question also posted on VAF and submitted to Van's technical support



  • Re: Blown Fuse

    by » 2 years ago

    The Heavy Maintenance Manual,  Chapter 76-10-00, Page 39, Shows the Location and purpose of each of the fuses.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Barry Bernstein

  • Re: Blown Fuse

    by » 7 months ago


    Did you ever get any idea of why this happened in the first place? 

    I have the EXACT same symptoms. And I mean exactly as you described with one exception; After changing the fuse to a new one and starting the engine, the fuse burns out again.

    When I install a new fuse and power up the plane on battery alone I have no issues with the light. After I start the engine for a few minutes and then shut down, the fuse is burned out and the Lane A light no longer illuminates


    Could this be bad ground somewhere? how could the little LED be pulling an excess of 2 Amps??


    The plane was recently repitched to spec and a dynamic prop balance was completed to .03ips.

  • Re: Blown Fuse

    by » 7 months ago


    Have you verified the values of the resistors at the LED indicator light?  When LED lamps are used, there should be a 1 K-ohm resistor in series with the LED, and a 1.5 K-ohm resister in parallel with that same LED. See section 24-00-00, page 31 of the 912iS installation manual.  I’ve heard of some folks who had a 1.5 ohm resistor in parallel instead of 1.5 K-ohm, which would blow the fuse.  

  • Re: Blown Fuse

    by » 7 months ago

    Wesley, there have been reports of the nuts that hold the ignition key and the spar-pin engagement light on the12iS coming loose and backing down all the way to the pc board, causing a short.  If you haven’t already done so, remove your PFD and the four screws holding the ignition module to the instrument panel, remove it and look at those nuts.  Just a wild thought, but others have had this issue.  I’ve wrapped nylon wire ties around my switch and light bodies to keep them from contacting the pc board should they come loose.

  • Re: Blown Fuse

    by » 7 months ago

    So the plane has functioned totally normally for 250 hrs so I suspect the resistors are all good. I've done a little multimeter testing and they show 1.5 K ohm resistance.

    I pulled the ignition module previously and didn't not any grounding points but ill pull it again today to see what I find. Thanks for the suggestions yall. This is a truly baffling problem as I did continuity tests starting at the LED light all the way back to ECU itself with nothing abnormal to note.

    The rotax manual reads like the power output is a digital signal and i cant imagine the computer just randomly starts to send a >2amp signal that blows the fuse.

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