Hi, while I am not a true auto o’scope jockey, I did use one professionally on a daily basis back in the 1990-2005 years.
I never tried using it on a positive ground system.
In my opinion you would just connect the battery leads to pos and neg according to the scope , not according to the system polarity. In other words, black to battery neg and (yellow?) to b+. Patterns may be inverted as compared to standard patterns but still accurate. Stand on your head or turn scope upside down.
This only works with 12 v. If you have a six v system you may need to hook battery leads to a stable converter or a 12 v battery.
I may have the owners manual somewhere in storage, I’ll keep my eyes open for it.
