Hmmm, I have never seen one like that, that I remember, in an O scale loco. Is this in a 4-4-0 maybe? That is a typical design I have seen on most older HO motors prior to cans.
In the photos, it appears that both brushes are mounted through insulated fittings. The top one obviously has no connection to the frame. I can't see the bottom one well enough to tell. I can see the insulted fitting however. So Check to make sure the bottom one has not strap to the frame of the motor or the loco frame. I'm guessing it does not.
I have a Max Grey PRR 4-4-0 that may have a motor like that. It has been a few years since I worked on it. I remmber it draws very little current and I was able to use a real small decoder (by O standards) in it. I think it is a Digitrax DH123. The loco draws well under 2 amps at all times.
If you want to discuss this in more detail, you can contact me via email from my profile.
