Not sure if you’re talking about readings when it’s running or stopped. You can’t really take resistance readings across windings etc because the resistance is so low that everything looks like a short circuit to a multimeter. I’m not really sure about the regulator wiring but across the rectifier section you should be looking at about 1.4V between any 2 wires. I think the whole thing is one package tho, so a multimeter will be useless.
When it’s running all you can really hope for is 14.4V across a charged battery at 2000rpm or so. Above 14.8 and you’ll fry the battery so you’ll need a new regulator. Less than 13.2V on even a flat battery and the fault could be anywhere in the system, but is much more likely to be the wiring. I’ll see if I can get some readings off of mine later, but since it’s running at 15.3V at the moment it might not be a good guide.
Oh, it might be a good idea to check the -ve line resistance between the battery and wherever you connect the black multimeter lead. Nothing screws up vehicle electrics like a dodgy earth.