BTW, the three easiest places to take measurements are : at the battery, from the accessory socket (if yours is working) , and up under the front fairing. If you have a tender on the battery, that is ideal as well. Whatever is easiest for you to get a voltage.
Now, here is what my Downtown does and what you should expect: When I turn the ignition on, the voltage is going to drop into the 11.x . After you crank, it will go to charging at 13.9 v to 14.4v. I would test the battery and then change the regulator if it ever dropped to below 13.2v charging at any point after startup. If my Downtown drops into the 10.x volts , it is iffy if it will start. Sometimes I get lucky. I dont mean to be disrespectful. I want you to find the problem , and fix it, and ride! After two weeks you are still scratching your head on it, and I think you are making it way too hard on yourself. When I decided to run heated clothing, I had to figure out what exactly the Downtown could do, lest I find myself at the side of the road frozen. I decided that I needed to know the state of the battery and charging at all times. So I put an accessory-to-SAE plug in the accessory port, and ran it to an SAE voltage indicator. Since then, I have kept an eye on it just like I do engine temp, etc. But even if you dont want to mount one somewhere, It is always good to have in your toolkit ($12) , and it will attach to your battery tender cable ($8) (which you should also install to do battery maintenance). You might already have done so! While my wheel is off for tire change, I am currently installing a second 15A cable with SAE end connector to the glove box. Unlike the accessory port fuse, this fuse will be accessible through the cable window in the tub. I used a fishtape to pull the wire from the front through the tunnel . You can see both the tender cable and soon to be glove box cable here: