how can I fix my ride on lawnmower?

I have a 6 year old Champion 6\64 ride on mower.
It starts Ok but cuts out when I try to engage anything at all .ie gears,cutters. I can overcome this problem by starting the mower then disconnecting the printed circuit board bypassing all safety devices controlled by micro switches ie seat pressure switch and grass basket. and I can't turn off mower untill I reconnect circuit board. ie I reconnect a plug with loads of colured wires.
If smeone knows of a wiring diagram I am sure I can sort it out as each wire must go to to micro switches
but I cant work them all out.
Thanks
Ian