To add, most multimeters (like free w/ coupon Harbor Freight one) don't have a "zero ohms" function, but still work fine. Just touch the leads together and note the "zero reading" and subtract it from subsequent ohm readings. I also don't recall the resistance of the "field windings" (between 2 terminals/brushes). I would guess the field draws <1 A, so probably 12 ohm or higher.
I does get tricky trying to measure <2 ohm accurately, such as trying to measure ground resistance. Often, for a large current like alternator output or starter draw, it is more telling to measure the voltage drop from the case to BATT- as the device is drawing current. In general, you want to see <1 V drop back to BATT- from all grounded cases (alt, Vreg, starter, engine block). I once saw the speedometer cable in my M-B smoking as I cranked the engine, an obvious sign of a corroded engine ground connector. A new alternator I installed in my 69 Dart didn't output current until I clipped a jumper cable from its case to BATT-, another sign of a bad return path (alt to block). Both were problems with oxidized aluminum that a little sanding fixed.
