Thanks for all your replys,
Ok, some more info.
I have tryed disengageing the auto throttle, and stall Guard, that didn't make any difference.
I have found that the seat switch is a normally closes type, and when you sit on the seat it creates an open circuit, so by my removing it all together everything works even the PTO. But still the engine wants to stall when I depress the HST pedal.
Our Tractor is a 2007 Grand L4240 Cab, with HST transmission, the serial number is 32037
I am not sure what generation it is, but I know that after we bought our tractor they came out with an improved pedal, that gave it a bit lighter feel, so making it less fatiguing to operate, I did ask if our tractor could be upgraded to that pedal, and was told that it wasn't possible.
I appreciate all the help given.
Dan Andrews