Essentially, I have one TIU and, at the time, only one AIU connected. I had 9 switches connected and working well. No accessories were connected. I had switched over from DCS engines to conventional and was just checking the switches which now seemed to have stopped working. Previously, when reading the track it would show 1 TIU and 1 AIU however it now shows 1 TIU and 6AIUs when there is still only one attached. (The connections are correct) I disconnected all of the switches from the AIU with the same result. I had one new AIU in the box and have since tested it with the TIU and when reading the track it correctly shows 1 TIU and 1 AIU. I am assuming there is something wrong with the AIU itself as it was previously working perfectly. I did see an old thread on OGR where someone raised the same issue. I didn’t see that it was ever resolved. If something internal has blown it is likely cost prohibitive to send it off for repair. I’m looking forward to hearing the results of this enquiry.