Voltage regulator for D68U

My '54 D6 8U charging system has me scratching my head.  Thinking the voltage regulator is bad, except that I can get it to work sort-of...  Naturally all my local parts places don't have decent books any more and can't cross the old CAT numbers.

The machine is pony start, hence 6V.  It's been pos. ground ever since I've owned it (and I kind of like it that way since all my other 6V machines are pos. ground) although I think CAT made her neg. ground.  The machine was laid up for about two years due to an engine issue but once that was sorted out she wouldn't charge.  Repolarization didn't take so I took the reg. apart, cleaned up the points and ground contact and it worked for a while then quit.  Now I have to repolarize each time I start up, it works for that run but the cutout relay will not open when I shut down (have to open the reg case and pull the relay points apart -- it does stay open after that though.)  No changes were made to wiring or anything electrical before vs. after the engine rebuild.  

If I remove the regulator and test the generator (on the machine, about half throttle) I get the following:  Field disconnected, Armature disconnected, A to Ground about 0.3 V, F to ground 0 V.  If I then ground the field I still only get about 0.3 V on Arm.  If I put batt. voltage to F (only for a moment) I get about 12 V on Arm -- this makes me think it's a B circuit gen. and is OK.

Questions:

1) Is the generator indeed a B circuit?  (tag missing)  Do you concur that it's OK?
2) Anyone have a current part number for the proper regulator?
3) Is the machine actually supposed to be neg ground?  If so is it really a huge sin to convert it to pos?  Is the polarity switch contributing to my problems? (although she ran fine that way for a decade......

Thanks in advance

Pete P.
Harborcreek, Penna.
 

Electrical dose not compute in my brain so I cannot help you make the regulator work. I us to fuss with the old regulators and generators and never had much luck 30 years ago finding parts or they where sky high priced. I have a D6 to use not as a restoration so I gave up and have a 12 V alternator if I want lights. If you just want to use the tractor and have it start with less drama use a 12 V battery and take it to the shop ever 2 weeks or so if you use the tractor regularly. Only starting twice a day have had 12 V last more than a month running 6 days a week.

But if you want original, hopefully someone has a source of parts.

Not a good idea to mix and match components and Cat used negative ground.
Depends on what generator you have. The Delco-Remy units use a type "A" regulator
The American Bosch units us a "B" type regulator.
The regulator needs to match the grounding of the system either pos or neg. Some can handle both.
The difference is in the point material which has the quality point contact to match polarity.
Dual polarity regulators use same point material both sides.