Possible stator or generator issue

Using a multimeter set to resistance (Ω) mode, short the leads together and note the reading.

Measure the resistance between each pair of the three yellow stator wires (1 to 2, 2 to 3 and 1 to 3), and subtract the reading you got with the leads shorted together.  The resistance of each stator pair should be quite low (something like 1Ω or less), and all three measurements should be very similar.  If one pair measures open circuit then you have a break in a stator winding, and if one pair measures significantly lower resistance than the other two then you may have a winding with shorted turns.

Next, measure between each stator wire and the engine case.  All three readings should be open circuit (usually "OL" on the screen).  If you see a low resistance then a stator winding is shorted to the case.

Check that the pins and sockets in the stator and regulator connectors are fully seated in their connector bodies.

If all of that checks out, then your problem is almost certainly elsewhere.  Not knowing how your airplane is wired it's hard to know where else to look, but some possibilities include a fuse or relay in the Fuse Box, the System B regulator or the ECU (wiring/connector pin issues are much more likely than the ECU itself).  The regulator is easily checked by substituting a borrowed, known-good unit.