That should have a transmission switch in the START circuit that is closed when in NEUTRAL. Disconnected, misadjusted or bad could cause the problems, along with being in gear. It should have Purple wires.

A loose connector on the PTO or Key Switch could cause this as well, OR those switches being bad.

Thanks for the information. I had another look earlier and found another switch which is located behind the deck lever for raising and lowering it......hard to tell if it's a dodgy switch as I'm not sure how to test it? So far I have cleaned the contacts on this switch and the seat switch and still no change. Regarding the transmission switch I did follow a set of wires which go all the way back and sit on top of the transmission......yet to roll the mower over for a closer look. Appears to be awkward to access it without lowering the rear axle assembly. I have done a test on the key switch with my test light and I get power from the battery to the switch as well as when I turn the key to the ON position I get power leaving the switch... and vice versa when I turn the key off

There should be a small terminal on the starter solenoid.

Jump 12V to that and it should crank if the battery, solenoid & starter + the "heavy" connections from the battery are good.

IF it cranks, you know the problem is between the key switch and the solenoid small terminal.

Cool thanks! I'll give that a go tomorrow :)

Thanks heaps for your help. I got a single piece of wire and went from the positive battery terminal to the exciter connection of the solenoid and it cranks the motor over. Least now I'm onto a winner :)