voltage regulator

I seriously doubt that the output driver of the original regulators would be a MOSFET.... since they weren't in existence or at least in common production then. The new parts? They could very well be.

As said, using an ohmeter on the regulator output to ground is unpredictable; it depends on the exact design, and even on how the meter is used and what polarity is used. There might be a couple of 'most common' designs...