That is the kick down solenoid. The number one cause of a UN commanded down shifts, is a defective kick down solenoid. The key here is the transmission is dropping down two gears; I would start by changing with the KD solenoid. It usually has a mechanical failure. Disconnecting the wire is not going to fix it, the solenoid may have an internal mechanical failure. You will have too change both pieces; the washer goes against the case.