Hillerbee states they have swopped the box and it works in the other aircraft. A simple suggestion. Maybe look very carefully at the lugs of the wires going onto the starter generator-especially the thin one going with the thicker one on one of the biggerstuds as well as the 2 thin wires on the smaller studs. I have burned out a GCU on a 105 twice until I found even though the lug was still attached and looked fine, there were a thin loose strand that once fitted shorted onto the next door neighbour stud and it was only when it cut my finger that I found it. One never knows with these things as it often turns out to be the simplest thing.