Damaged IR cable
Had the same problem ... except the leads just pulled out of the "connector" to the logic board
This also happened with the connector to the "fan" ... was able to get a new fan with the connector which I was then able to re-connect the fan to the logic board
The SSD which I installed went out couple days back ..
Removed and have been using for two days, in an external USB 3.0 with no problems
Putting together just now .. dropped one of the small screws used to connect the "wifi cover"
When pulling the logic board back ... the leads "pulled" out of the connector on the logic board
The "connector" to the logic board in both the cases of the "fan" and the "sensor connector" had become "brittle" and stuck together .. would not separate and caused a failure in both cases
Now I looking for a new "sensor cable" in able to correct this problem
Any help would be appreciated
Will be removing the remaining parts of the mac mini .. the logic board is out