But I said that it's not connected to any motor nerves, so it has no decisions to make.

Neither are most supercomputers connected to motor nerves, yet people are quite interested in their output!

Well, I suppose it can still decide what to think about, so let's say I also remove that ability and force its thoughts to drift randomly.

In that case, it's no longer clear if "pain" is even well-defined. Something whose thoughts truly drift randomly and are prevented from attaining any order ... is in a state of entropy; it does not even count as a control system, let alone life.