Since the sensor and activation module system work off a percentage, as I'm sure you're aware, it means the logic goes like this:
4/4 activation modules active is detection of 100%
3/4 activation modules active is detection of 75%
2/4 activation modules active is detection of 50%
1/4 activation modules active is detection of 25%
0/4 activation modules active is detection of 0%

Connecting the activation module to thrusters it will correctly detect 0% speed and output an active signal.

However, once the ship accelerates above 0% the activation module still outputs an active signal, this is wrong, it should turn off its active signal.

In the case of thrusters this would easily allow detection of movement; something currently not possible due to this bug. In my particular case, and how I discovered this bug, I was attempting to have the engines light up whenever the ship was moving; make it look like there was actually a use for those big engines. The closest I was able to achieve was to connect 100 activation modules, 1 active, 99 inactive to the sensor. This was a waste of space in my ship and only provided detection of 1% speed, which on a normal server with max speed of 225 would be 2.25. My ship is quite slow to move, so I was moving for 5-10 seconds before the engine lights turned on, it looked absurd. I did some math and in order to get my ship to look right, the engines come on as early as possible, I needed to get no more than 0.1% speed detection. To get that percentage would require a minimum of 1000 activation modules, which in turn feeds back to mass and acceleration issues.