I use a dressmaking pin and two clip leads and my ohmmeter. One clip lead goes to one end of the winding, the other clip lead holds the pin. I carefully use the pin to probe the various field coils till I find where the open is located. A sharp pin can penetrate the insulation on the individual wires without shorting anything, if you don't have a ham hand. I usually find the non-resetting fuse at one end or the other of the windings, they don't seem to put them in the middle.