2 Strokes Down Under

Hi Guys
My 99 RS250 will not fire on the top cylinder for some reason. I have gone through air and fuel and think it is spark related. In anticipation of the worst does anyone know whether the black box off a similar vintage RGV 250 will fit the RS250 or is the programming different?
Many thanks
PK

Interchange no problem. Have you tried earthing the coils back to the negative side of the battery from the
mounting bolt

Thanks for the suggestion. I did all the contacts and cleaned up a heap of grime. In the end I had a clogged jet (duh!!) but it also now starts on the button so I think of benefit alround.