Lighting Coil

Dear Tech Guy!
I am about at my wits end.  Here is my problem, in as few a words as I can describe it.
I have a Rotax 447 with 300 hrs.  It is 3 years old.  About a month ago, I landed in a place that was a bit muddier than I originally thought.  My tires threw some mud when I took off, although it wasn't that bad.  Just before I took off, I noticed that all of my electrical accessories had quit working.  I don't know whether it has anything to do with the muddy field or not.  About 10 seconds after takeoff, my accessories came back on...for about another 10 seconds, then off for good.
I have returned to the airport to start the engine 3 times since, to no avail.  I checked AC voltage on the input side of my Key West regulator, and the reading was "0".  I checked DC voltage on the output side of the regulator, and again, the reading was "0".  Both times, with the engine running at idle.  I then connected a 12 volt battery to the output side, and all of my accessories worked just fine.  My EIS read 12.8 volts.  I then disconnected the lighting coil wires from the regulator, and tested AC voltage again.  This time, I ws reading 6 to 8 volts AC at idle, and approx. 12 to 13 volts at what I guess was about 3500 rpm.
I assumed that the problem was the regulator, so I ordered another one.  I hooked it up this evening, and still nothing works.  I don't know what to troubleshoot next.  How likely is it that there is an internal problem with the magneto(s)?  Is there any other test I can do to locate the problem?  I did connect a battery to the DC side again tonight, and still, the accessories work fine.
Thank you - Max Rentz Newark, OH

Tech Guy Responds
Hi Max,
It sounds like you have a case of an open circuit lighting coil.  Now the Ducati lighting system is normally very reliable,  since the output of the lighting coil is a low voltage high amperage AC output the coil windings are very thick and relatively few in comparison to the ignition circuit.  This normally ensures a trouble free coil for the life of the engine.  The two yellow wires that exit the lighting coil are attached to a series wound coil that is floating, meaning non internally grounded. The trouble shooting procedure for the lighting circuit is rather straight forward and simple.  First do a resistance/continuity test between the two yellows with nothing else connected to them. The resistance with an accurate VOM should be approx 0.1-.2 ohms.  This will tell you if your coil is continuous and that the wire resistance or length is correct. If this is what your coil shows the next test is a short to ground test, take one lead of your ohmmeter and attach it to one of the yellow coil wires and the other to ground, there should be no continuity whatsoever.  Next test the other yellow wire by attaching one ohm meter lead to it and the other to ground and again you should have no continuity. This indicates the coil is not shorted to ground.  The last test is with the engine running and this is an unloaded AC output test. When connecting you VOM between the two yellows with nothing else attached to them and the meter set to AC volts, you should see an AC reading of approx 12-20 volts at idle, next as you rev the engine up you should see an AC output of around 30-40 volts.  If the coil passes all of these tests then chances are the lighting coil is good and the problem remains in the wiring, accessories, or the voltage regulator of the plane.
Again it is rare to see any lighting coil fail , the most common causes of failure are due to winding damage caused by  incorrect length screws being used to remove the flywheel.  Unfortunately this is rather common for novice repairmen.
Good luck with your lighting dilemma and I hope I have been of some assistance to you.
Blue skies and great flying - Gordy