Ariel Owners Motorcycle Club

Where does the black wire, which is connected to the D terminal, actually go to?

D should be yellow, f green

Dave

Chris Sealy wrote: Thu Jul 09, 2026 3:37 pm Where does the black wire, which is connected to the D terminal, actually go to?

There should be two wires coming from the field coil, one goes to earth and one to the F terminal.

Then there are the two brushes - one is connected to the D terminal, the other to earth.

Ok, today’s exciting instalment. Checked continuity separately between F/D terminals to commutator, all good. Rotated comm slowly by hand with test probe on the comm and ground, all good. Tried Chris’ idea, connected a 6V battery, neg to F terminal, pos to ground on body, to my surprise the generator rotated slowly, ( only a small battery) but it was quite happy rotating in the correct direction. This indicates to me that the field coil and armature are fine? To add to the mystery the total resistance as connected is 2.7 ohms, which according to the manual is spot on, so no apparent issue with the D coil? Locked F/D and connected to a battery, a slight kick of the armature but no rotation. Dont know where to go from here. I am thinking of replacing the F/D coils, are these available? Any assistance appreciated, I want to install the generator so that I can finish rebuilding the engine.

Can you take a picture showing all the wiring? If it rotates with the battery between the f terminal and the ground, it sounds like it's not wired up correctly internally. There must be some connection somewhere to the commutator for the armature to rotate - it sounds like you have the f terminal connected to one of the brushes as well.

To repeat, there are two wires coming from the field coil. One of these is grounded, the other goes to the f terminal. Then there are two brushes - the wire from one of these is grounded, the other one goes to the d terminal.

Ok, today’s exciting instalment, tried attaching a battery to the field coil only in an attempt to re-magnitise the coil. Negative to the F terminal, Pos to the ground. The armature started spinning, slowly, but steady, no apparent distress. Checked continuity from F/D terminals to comm, all good. Rotated the armature with probe on the com and the other grounded. All ok, nothing untoward. It appears the field circuit is fine but still no output. I am at a loss to figure this out. Any assistance appreciated

Sincere thanks to all that have offered advice. Having just dismantled the generator ( again!) I think the internal wiring may be the issue. I have posted photos but to clarify, The F terminal wire goes directly to the coil, the other end of this coil is connected to the second coil. The wire exciting the second coil is the wire going to the D terminal. One brush is connected to ground, the second brush is also connected to the D terminal. This is how I got the bike, the only item I have changed is to convert the 2 bullet type connectors to nut and bolt terminals, rather than solder/unsolder the F terminal every time it is dismantled. This does not match the advice from Simon, so I am assuming this is wired incorrectly? Hopefully this is the answer. Thanks.

Have a close look at this...

Hi

I would try connecting the wire from the coil, (not the F wire), to ground or to the other brush, (not the one connected directly to D)

Regards Mick

As Mick says, The Field coil wire; which looks to have been extended; should not be connected to the D terminal. It must be connected to the body of the dynamo. I believe that this is your only problem.
One of the brushes is earthed. You could connect The Field wire to the same point.