Maybe I got unlucky with my modules, I checked them with two DMM's and this http://www.banggood.com/0_28-Inch-2_5V-30V-Mini-Digital-Voltmeter-p-974258.html. All showed the same readings +-0.01V.
you are so clever！！
This is definitely a great mod! It’s too bad there’s frozen snow on the ground here and I couldn’t use it until 2016. But it’s definitely something I would want to do on my MTB. (Right now I just use the TwoFish mount + EDC)
I can 3D print trapezoidal threads that actually work out of ABS or various Nylon grades. I am picturing the setup as done the same way out to the ports, but then a final larger cap would thread over that end, snug to the tube ID, so you don’t have to use rubber port plugs (those port plugs are great though, for keeping smartphone jacks clean).
Well, what if you print a cap with threads on the outside and a ring (matching the inner diameter of the sterer tube) with threading on the inside, and glue the ring into the sterer tube so you can screw in the cap?