"Which voltage" Try to get as close to the VR blue wire as you can. The point you mentioned at 14.6 is it. This shows the VR is close. Also, you must measure "warmed up" for accuracy, because the VR is temperature compensated. Look in the service manual. 13.8--14.2 warm is optimum. Much over 14.5 warm you need to look into.
IT IS NEARLY ALWAYS voltage drop between the battery and the VR blue wire terminal, "ign" terminal.
Another way to measure this is to turn the engine off, but turn the key to "run." Put your meter, one probe right on the battery POS post, and the other "as close" to the VR ign terminal as you can get. The ballast, originally, or the alternator field blue wire. You are directly measuring the drop in the harness, all the way from battery to the VR. You are hoping for a very low reading, the lower the better. More than .3V or so (3/10 of one volt) you need to look into things. This is why I occasionally suggest a relay to run underhood ign loadds.