Earlier in the year, I had repaired chewed up field coil leads. I reattached broken wires, insulated etc. I'm confident of my repairs because I have continuity and no shorts to ground.
When it came to attaching the leads to the two terminals, might I have done it backwards?
If I did attach leads to opposite terminals, north poles would become south poles.
Does the dynamo "care" which way the current flows through the field windings? I know the starter motor doesn't "care" about the polarity, it spins fine with pos or neg ground.
David

headlight method is putting a bulb in serie with the coils but you have to put cardboard between the bushes and the ancre. It should not be connected to the system while doing this.

Replace the bobine (french for coil) burned out.

My experience of the 6V Paris Rhone (and I think the Ducillier is similar) is that you can't 're-flash' the dynamo as it stands. You have to disconnect both of the loom wires from the dynamo. Remove the field wire from the brush post. Then run a temporary wire from the battery positive to the field terminal post on the dynamo. Now flash the other end of the field coil to earth (the end which was connected to the brush post). Do not flash for more than a couple of seconds or you will burn out the field coil(s). If the dynamo is still reverse polarity, swap the temporary positive wire to the 'brush' end of the field coil and flash the other end to earth.

I'm making electricity!
I made every possible check of the dynamo for continuity, grounding, shorts, opens, etc. I flashed the coil through the armature, through the field terminal, field wire to field wire, forward, backward and probably even sideways.
Do something, run it, check it. Do something else, run it check it. Repeat at least a dozen times.
Then I decided that it's not the dynamo, and ordered a new regulator. I bought a cheap, new, 6 volt, neg ground, A-circuit regulator.
It arrived today, I put it on, and I'm making electricity. It shows a positive rate of charge, and the warning light goes out. With all the lights on, I show about 20 amps discharge. With the engine running, it comes back to Zero.
Pam and I drove it about a mile today. finally!

great.