Hi Chas,
while i'm not the next C5's electronics genius i do know how a torch works
i think we need a bit more information,
what was the need for changing the old control box out?
did the C5 run with the new box?
1) was the original faulty?
2) was you just testing a spare?
if 1) was ok, might be that the 'new' box is iffy. if you can, try it out on a working C5.
regs
alan