I had the same issue on mine and it was the Bradley box (large electronics module under the fuse area).
I hope it is not the same for you and it is something more simple like a relay, as when I replaced my module it was very expensive and I was told was the last one they had with no more replacements to be made..
This is however on an S1, so it is entirely possible the S4 is different.
Also - Welcome back!
