Hi guys,
Measured field coil resistance, i read 4.0
Manual says 4.9 +- 10%
Guessing this is broken?
The field coil is pretty foolproof, it's just a hunk of iron with wire wrapped around it creating an electro-magnet. When energized it generates the magnetic field that makes the alternator work. This is the part that requires your battery to be fully charged in order for the alternator to function. I do not know how this component could be the source of your problem. You can test it by putting power to it (white and green from the alternator harness) and see if a wrench (or other bit of iron) will stick to the alternator cover.
The stator coil is what generates the charging current and creates the most load. I suggest you follow the procedure for testing the AC output of the stator coil. I would disconnect the rectifier for this test so you don't fry another one (you have to disconnect the yellow wires to test the AC output of the stator anyway).
