I suggest you check your hard drive jumpers. There should be only one Active drive. If you disconnect the data partition the Active partition will be changed. We are not clear why the partition will be Active partition when you connect it.
Defect detector — Overview of a wheel impact detector installation A defect detector is a device used on railroads to detect axle and signal problems in passing trains. The detectors are normally integrated into the tracks and often include sensors to detect… … Wikipedia