912iS Dual Flashing Lane Light at Startup

Jeff gives excellent advice above.  The 912iS stator is a three phase Delta-wound device and the regulator contains a three-phase rectifier.  Unlike in a single phase system, loss of one phase in a three phase system will not necessarily cause a total loss of DC generating capability, but it may cause high current overstress of the remaining phase coils and rectifying diodes.

When you do the tests, be sure to use the meter's resistance (ohms, Ω) setting and not the continuity test function.  Before testing, short the meter test leads together firmly and observe the meter reading; this is your "zero ohms" value.  You'll subtract that value from whatever you measure during the tests.

The stator coils are very low resistance, so the measurements with a hand-held meter won't be super accurate, but that's OK.  You just want to be sure that none of the output wires are shorted to the engine crankcase (they should measure infinite resistance) and that they have similar low-ohm measurements between all three wire pairs (1-2, 1-3 and 2-3).  If one wire pair measures about double the resistance of the other pairs then you have a broken coil in the stator between those two wires.

Thanks, Jeff-

Prior to replacing Reg A, I had unplugged the gray connector and tested resistance pin-pin on the engine side. All readings were <1Ω. 

I did not test the three leads that go to the stator to engine ground. Happy to do that next time I am at my hangar. 

I would do so Mark, as Eric explained very clearly, there can be a partial failure of the stator.  The ground test is the most important to do because a phase coil can develop a high resistance short to ground before it completely fails. Sometimes it may not even show up with a simple ohm meter because there is not enough voltage from the meter to overcome the resistance. But it's still better than not doing the test.