red is positive on a negative ground system
There are 2 battery terminals. A positive or hot and a negative or ground. The positive is slightly larger than the negative.
Batteries are neither positive nor negative ground. It is the circuit itself that determines the common ground. For example: If I have two circuits, one needing 6vdc negative ground and the other needing 6vdc positive ground, the battery would be installed the same way in both circuits (positive terminal on the battery to the positive connection in the circuit, regardless of whether the circuit is positive or negative ground). The reason for labeling the ground as Positive or Negative has more to do with how the circuit is wired up, than the actual voltage source. The explanation for that is beyond the scope of this answer.
Electrical sytem positive ground
The quickest and best way is to look at the battery. If your positive cable (+) is going to the frame or body, positive ground. If the negative (-) goes to the frame or body, negative ground. I believe that a MF 35 is a neg ground system but use the check from above.
Negative - (Black) is Ground, Positive + (Red) is Hot. Ground wire goes to Negative (Black) it goes from negative on battery to engine for ground.
The 1937 Oldsmobile is negative ground.
Cars in which the positive terminal of the battery is connected to the chassis. They require specially designed components built for positive ground cars. The usual configuration is a negative ground (the negative battery terminal connected to the car's chassis).
Red cable to positive, black cable to negative.
positive
The negative battery terminal is on the battery. They don't have a wire coming from it like they do the positive. For charging purposes, the engine block acts as the battery ground. When disconnecting the negative at the battery, the negative terminal usually has a black wire and the positive has a red.
I doubt it but I am not 100% sure. It is unlikely in 1983 BMW was using a positive ground system. You can easily find out. Trace the negative battery cable and see where it goes. It is is attached to ground then it is a negative ground system.